Upgrade therubyracer to get a version of libv8 that will install

I can't get the old version of libv8 to install on my ruby 2.1.3. This
newer version installs fine, though.

Gemfile

@@ -11,7 +11,7 @@ group :assets do
   gem 'coffee-rails',           "~> 3.2.2"
   gem 'uglifier',               "~> 1.0.0"
   gem 'jquery-ui-rails',        "~> 2.0.0"
-  gem "therubyracer",           "~> 0.11.3"
+  gem "therubyracer",           "~> 0.12.1"
 end
 
 gem "haml",                     "~> 3.1.4"

Gemfile.lock

@@ -134,7 +134,7 @@ GEM
     json (1.8.1)
     launchy (2.4.2)
       addressable (~> 2.3)
-    libv8 (3.11.8.17)
+    libv8 (3.16.14.7)
     libxml-ruby (2.6.0)
     mail (2.5.4)
       mime-types (~> 1.16)
@@ -244,8 +244,8 @@ GEM
       multi_json (~> 1.0)
       rack (~> 1.0)
       tilt (~> 1.1, != 1.3.0)
-    therubyracer (0.11.4)
-      libv8 (~> 3.11.8.12)
+    therubyracer (0.12.1)
+      libv8 (~> 3.16.14.0)
       ref
     thor (0.19.1)
     thread_safe (0.3.4)
@@ -333,7 +333,7 @@ DEPENDENCIES
   sass-rails (~> 3.2.5)
   show_me_the_cookies (~> 2.0.2)
   simplecov (~> 0.4.0)
-  therubyracer (~> 0.11.3)
+  therubyracer (~> 0.12.1)
   tire (~> 0.4.1)
   twitter (~> 5.11.0)
   tzinfo (~> 0.3.29)