title: Can't add sources with gem
body: <p>I'm trying to add <a href="http://rubygems.org/" rel="noreferrer">http://rubygems.org/</a> in my sources because I can't use 'gem install NAME' (this error : Could not find a valid gem 'dashing' (>= 0) in any repository).</p>
  
  <p>So, I did this command : gem sources -a <a href="http://rubygems.org/" rel="noreferrer">http://rubygems.org/</a></p>
  
  <p>the result : ERROR:  While executing gem ... (Gem::OperationNotSupportedError)
      Not connected to a tty and no default specified</p>
  
  <p>I give you my ENV :</p>
  
  <pre><code>    $ gem env
  RubyGems Environment:
    - RUBYGEMS VERSION: 2.4.5.1
    - RUBY VERSION: 2.2.4 (2015-12-16 patchlevel 230) [i386-mingw32]
    - INSTALLATION DIRECTORY: C:/RailsInstaller/Ruby2.2.0/lib/ruby/gems/2.2.0
    - RUBY EXECUTABLE: C:/RailsInstaller/Ruby2.2.0/bin/ruby.exe
    - EXECUTABLE DIRECTORY: C:/RailsInstaller/Ruby2.2.0/bin
    - SPEC CACHE DIRECTORY: C:/Users/mramart/.gem/specs
    - SYSTEM CONFIGURATION DIRECTORY: C:/ProgramData
    - RUBYGEMS PLATFORMS:
      - ruby
      - x86-mingw32
    - GEM PATHS:
       - C:/RailsInstaller/Ruby2.2.0/lib/ruby/gems/2.2.0
       - C:/Users/mramart/.gem/ruby/2.2.0
    - GEM CONFIGURATION:
       - :update_sources =&gt; true
       - :verbose =&gt; true
       - :backtrace =&gt; false
       - :bulk_threshold =&gt; 1000
       - :sources =&gt; []
    - REMOTE SOURCES:
    - SHELL PATH:
       - C:\Users\mramart\bin
       - C:\Program Files (x86)\Git\mingw32\bin
       - C:\Program Files (x86)\Git\usr\local\bin
       - C:\Program Files (x86)\Git\usr\bin
       - C:\Program Files (x86)\Git\usr\bin
       - C:\Program Files (x86)\Git\mingw32\bin
       - C:\Program Files (x86)\Git\usr\bin
       - C:\Users\mramart\bin
       - C:\RailsInstaller\Git\cmd
       - C:\RailsInstaller\Ruby2.2.0\bin
       - C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common
       - C:\Tcl\bin
       - C:\ProgramData\Oracle\Java\javapath
       - C:\WINDOWS\system32
       - C:\WINDOWS
       - C:\WINDOWS\System32\Wbem
       - C:\WINDOWS\System32\WindowsPowerShell\v1.0
       - C:\WINDOWS\System32\WindowsPowerShell\v1.0
       - C:\Program Files (x86)\Lenovo\Access Connections
       - C:\Program Files\nodejs
       - C:\Program Files\Java\jdk1.7.0_79\bin
       - C:\Program Files (x86)\Heroku\bin
       - C:\Program Files (x86)\git\cmd
       - C:\Program Files\TortoiseSVN\bin
       - C:\Program Files\PostgreSQL\9.5\bin
       - C:\Program Files (x86)\scala\bin
       - D:\gatling-charts-highcharts-bundle-2.1.7\bin
       - C:\Program Files (x86)\sbt\bin
       - %USERPROFILE%\.dnx\bin
       - C:\Program Files\Microsoft DNX\Dnvm
       - C:\Program Files\Microsoft SQL Server\130\Tools\Binn
       - C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit
       - C:\Users\mramart\AppData\Roaming\npm
       - C:\Program Files\Java\jdk1.8.0_73\bin
       - C:\apache-maven-3.0.5\bin
       - C:\Program Files\PostgreSQL\9.5\bin
       - C:\Program Files\MongoDB\Server\3.2\bin
       - D:\liquid
       - C:\Users\mramart\AppData\Local\atom\bin
       - C:\Program Files (x86)\Git\usr\bin\vendor_perl
       - C:\Program Files (x86)\Git\usr\bin\core_perl
  </code></pre>
  
  <p>None sources executing : gem sources</p>