don't specify ruby version in Gemfile

so that travis can run agains different versions

Author: artemave

Gemfile

@@ -1,7 +1,5 @@
 source "https://rubygems.org"
 
-ruby '2.2.1'
-
 gemspec
 
 gem 'pg'

app.json

@@ -5,5 +5,8 @@
   "keywords": ["REST", "testing", "stub"],
   "addons": [
     "heroku-postgresql:hobby-dev"
-  ]
+  ],
+  "env": {
+    "CUSTOM_RUBY_VERSION": "2.2.1"
+  }
 }