[build] adjust Gemfile for running (tests) on MRI

Author: kares

Gemfile

@@ -1,12 +1,12 @@
 source 'https://rubygems.org'
 
 # Specify your gem's dependencies in the gemspec
-gemspec
+gemspec if defined? JRUBY_VERSION
 
 gem "rake", require: false
 
 # for less surprises with newer releases
-gem 'jar-dependencies', '>= 0.3.11', require: false
+gem 'jar-dependencies', '>= 0.3.11', platform: :jruby, require: false
 
 gem 'mocha', '~> 1.4', '< 2.0'