add dependence of therubyracer

Gemfile

@@ -12,7 +12,7 @@ gem 'uglifier', '>= 1.3.0'
 # Use CoffeeScript for .coffee assets and views
 gem 'coffee-rails', '~> 4.1.0'
 # See https://github.com/rails/execjs#readme for more supported runtimes
-# gem 'therubyracer', platforms: :ruby
+gem 'therubyracer', platforms: :ruby
 
 # Use jquery as the JavaScript library
 gem 'jquery-rails'

Gemfile.lock

@@ -63,6 +63,7 @@ GEM
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
     json (1.8.3)
+    libv8 (3.16.14.17)
     loofah (2.0.3)
       nokogiri (>= 1.5.9)
     mail (2.6.4)
@@ -104,6 +105,7 @@ GEM
       thor (>= 0.18.1, < 2.0)
     rake (11.3.0)
     rdoc (4.3.0)
+    ref (2.0.0)
     sass (3.4.22)
     sass-rails (5.0.6)
       railties (>= 4.0.0, < 6)
@@ -124,6 +126,9 @@ GEM
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
     sqlite3 (1.3.12)
+    therubyracer (0.12.2)
+      libv8 (~> 3.16.14.0)
+      ref
     thor (0.19.4)
     thread_safe (0.3.5)
     tilt (2.0.5)
@@ -153,6 +158,7 @@ DEPENDENCIES
   sdoc (~> 0.4.0)
   spring
   sqlite3
+  therubyracer
   turbolinks
   uglifier (>= 1.3.0)
   web-console (~> 2.0)