Trying to run a Sinatra app and I keep getting this error:

```
/Users/matthewsmith/.rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems/specification.rb:2064:in `raise_if_conflicts': 
Unable to activate sinatra-contrib-1.4.2, because tilt-2.0.1 conflicts with tilt (~> 1.3) (Gem::LoadError)
from /Users/matthewsmith/.rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems/specification.rb:1262:in `activate'
from /Users/matthewsmith/.rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems.rb:196:in `rescue in try_activate'
from /Users/matthewsmith/.rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems.rb:193:in `try_activate'
from /Users/matthewsmith/.rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:132:in `rescue in require'
from /Users/matthewsmith/.rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:144:in `require'
from app.rb:3:in `<main>'

```

This is my Gemfile:

```
gem 'sinatra', '~> 1.4.5'
gem 'activerecord'
gem 'pg'

```

I tried including 

```
gem 'tilt', '~> 1.3' 

```

in the Gemfile as well but that didn't work.  

Any ideas?