Add execjs and rubyracer to Gemfile, should resolve #12

Gemfile

@@ -24,3 +24,6 @@ platforms :mri_18 do
 end
 
 gem "rake", "~> 10.1.0"
+
+gem 'execjs'
+gem 'therubyracer', :platforms => :ruby
\ No newline at end of file

Gemfile.lock

@@ -28,6 +28,7 @@ GEM
     i18n (0.6.9)
     json (1.8.1)
     kramdown (1.3.3)
+    libv8 (3.16.14.3)
     listen (1.3.1)
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9)
@@ -79,6 +80,7 @@ GEM
     rb-kqueue (0.2.2)
       ffi (>= 0.5.0)
     redcarpet (3.1.1)
+    ref (1.0.5)
     rouge (1.3.3)
     ruby18_source_location (0.2)
     sass (3.2.17)
@@ -92,6 +94,9 @@ GEM
     sprockets-sass (1.0.3)
       sprockets (~> 2.0)
       tilt (~> 1.1)
+    therubyracer (0.12.1)
+      libv8 (~> 3.16.14.0)
+      ref
     thor (0.18.1)
     tilt (1.4.1)
     uglifier (2.4.0)
@@ -102,6 +107,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  execjs
   middleman (~> 3.2.0)
   middleman-gh-pages
   middleman-livereload (~> 3.1.0)
@@ -109,4 +115,5 @@ DEPENDENCIES
   rake (~> 10.1.0)
   redcarpet (~> 3.1.1)
   ruby18_source_location
+  therubyracer
   wdm (~> 0.1.0)