Split up development dependencies.

Gemfile should include all dependences. The Gem Specification is meant
to build an end user package, not a src package. For development purposes
the git repository is to be used.

Gemfile

@@ -1,3 +1,8 @@
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
 gemspec
+
+group :development do
+  gem 'rspec', '~> 3.5'
+  gem 'rake', '~> 11.3'
+end

stanford-core-nlp.gemspec

@@ -1,5 +1,5 @@
 # -*- encoding: utf-8 -*-
-$:.push File.expand_path('../lib', __FILE__)
+$LOAD_PATH.push File.expand_path('../lib', __FILE__)
 
 require 'stanford-core-nlp'
 
@@ -18,9 +18,8 @@ recognition and coreference resolution for English. }
   s.files = Dir['lib/**/*'] + Dir['bin/**/*'] + ['README.md', 'LICENSE']
 
   # Runtime dependencies
-  s.add_runtime_dependency 'bind-it', '~>0.2.7'
+  s.add_runtime_dependency 'bind-it', '~> 0.2.7'
 
-  # Development dependency.
-  s.add_development_dependency 'rspec'
-  s.add_development_dependency 'rake'
-end
+  # license
+  s.license = 'GPL-3.0'
+end