Issue title: RSense Brackets
 Issue body: Started with a RSense  integration for Adobe's Brackets editor (see: https://github.com/tdegrunt/brackets-ruby-rsense-hints), but I'm running into trouble when posting stuff to the rsense server (see below).
Do you have any suggestions?

```
ArgumentError: invalid byte sequence in UTF-8
            match at org/jruby/RubyRegexp.java:1680
            match at org/jruby/RubyString.java:1732
    check_shebang at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:140
            rload at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:112
         rrequire at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:160
             each at org/jruby/RubyArray.java:1613
         rrequire at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:159
       initialize at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:60
             call at org/jruby/RubyProc.java:271
             call at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command/special_meth.rb:12
   visitFCallNode at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command/graph.rb:72
            rload at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:116
     load_builtin at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:198
             each at org/jruby/RubyArray.java:1613
     load_builtin at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:197
          prepare at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:309
  prepare_project at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:337
            clear at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:320
       initialize at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command.rb:90
             load at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/lib/rsense/server/command/preload.rb:13
   projman_set_up at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/bin/_rsense.rb:72
           (root) at /Users/tdegrunt/.gem/ruby/2.1.5/gems/rsense-server-0.5.18/bin/_rsense.rb:76
```

 Comments: 
 Comment 0: I'd throw a `puts` in here: https://github.com/rsense/rsense-server/blob/master/lib/rsense/server/command.rb#L140 and find out what the `source` arg is in the case where it errors. It may be something we need to account for in rsense-server.
 Comment 1: It looks fine (a very long dump), just source code, until this:

```
metadata.gz0000444000000000000000000000353312444653612013451 0ustar00wheelwheel00000000000000?W?T?Yߏ?4~?_a??nrwmQY	D)T?R? y?ٍ????????????M?ع?x???;?n?ol?????j?"????v?TQ???T?e?yZ)???%
?D???:???∾ws???ͤ??abS?i4???XY?߽????.??m?ֽ?????cͱA??%\?M?T?@???R?a\?|????;.??{?[?t?](???6??=?gy͐"??L??????e˩"T????1tÁ0a@mi?&?g??{:??Ц????hK.ѹ??o?䠐CC???W/??@zW??®jD??????o?%-?T4W?,?-?-/?=???g??????b?????gW?`?????=?ݜ?7??=e??׫?Ϟ?&άweE0??6????3H_ϡ?˝??8VZh??P{?3.7*U?b4?f(vs+k??+??t?٢?Q??+?Ux?????>2c6Y#J??&Y]>??Rp
                                                                                                                                               ?P?R}?A?3,9?F*??V?
                                                                                                                                                                 ??<s??????x7?s3Ys?7?9?2^

.
.
.

checksums.yaml.gz.....
```

I've been looking for gz files in my gems path:

```
⇒ find . -type f -name ½*gz                                                                                                                     ./passenger-4.0.56/download_cache/support-x86_64-macosx-10.10.tar.gz
./passenger-4.0.56/download_cache/webhelper-1.6.2-x86_64-macosx-10.10.tar.gz
./passenger-4.0.57/download_cache/support-x86_64-macosx-10.10.tar.gz
./passenger-4.0.57/download_cache/webhelper-1.6.2-x86_64-macosx-10.10.tar.gz

⇒ pwd
/Users/tdegrunt/.gem/ruby/2.1.5/gems
```

Maybe that's the problem that it should only use .rb files?
 Comment 2: aha, so I think we need to add .gz to this blacklist:
https://github.com/rsense/rsense-server/blob/master/lib/rsense/server/command.rb#L98

Anything else you can think of?

 Comment 3: Not entirely sure, but I see files with .md, .txt, .rdoc, .lock (Gemfile.lock), .sqlite3, .rst, .pem, .py, .gif, .png, .coffee, .mab, .scss, .less

Can't think of a scenario where you would want completion from those?

I've also seen stuff like:

```
./web-console-2.0.0/test/dummy/tmp/cache/assets/development/sprockets/13fe41fee1fe35b49d145bcc06610705
./web-console-2.0.0/test/dummy/tmp/cache/assets/development/sprockets/17c571144b4e44da39bddb2d2c412414
./web-console-2.0.0/test/dummy/tmp/cache/assets/development/sprockets/2b96b037f3dfeccfe27113eb95b06ea1
./web-console-2.0.0/test/dummy/tmp/cache/assets/development/sprockets/2f5173deea6c795b8fdde723bb4b63af
```

Gems like passenger, rails, sprockets, ruby-graphviz,  tilt, tzinfo, twilio-ruby and web-console are really including a lot of stuff. They might serve as examples of what not to include. 

Perhaps it's even better to switch it around: What should really be included? Would a .rsense file help configure this in user space?

 Comment 4: Wanted to think about this a bit before deciding about it.

Yeah, I think the potential for unknown filetypes to cause errors is too difficult to deal with via a blacklist. So I think you are right about using a whitelist, with a possibility to configure other filetypes in the .rsense file. So if you have just started using some new dsl with .myfunkydsl as the file extension, you can add .myfunkydsl into some field in a .rsense file and get rsense to recognize it. And I can try to whitelist everything I can think of on the front end.
{'source': 'GithubIssues', 'repo_name_with_owner': 'rsense/rsense', 'issue_id': 54171139, 'repo_stars': 298.0}