Upgrade safe_yaml gem, install javascript runtime for rails admin

The version of safe_yaml being referenced in the Gemfile.lock (0.9.2)
no longer exists on rubygems, likely due to a security vulnerability.

RailsAdmin includes some CoffeeScript assets which requires a javascript
runtime in order to translate/compile correctly.  Using 'therubyracer' for
now which uses Google's V8 javascript engine.

Gemfile

@@ -164,7 +164,7 @@ group :assets do
   # gem 'coffee-rails', '~> 3.2.1'
 
   # See https://github.com/sstephenson/execjs#readme for more supported runtimes
-  # gem 'therubyracer', :platforms => :ruby
+  gem 'therubyracer', :platforms => :ruby
 
   # Minify assets.  Requires a javascript runtime, such as 'therubyracer'
   # above. You will also need to set 'config.assets.compress' to true in

Gemfile.lock

@@ -131,6 +131,7 @@ GEM
       activesupport (>= 3.0.0)
     libnotify (0.8.0)
       ffi (>= 1.0.11)
+    libv8 (3.11.8.17)
     listen (1.1.4)
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9)
@@ -224,6 +225,7 @@ GEM
       ffi (>= 0.5.0)
     rdoc (3.12)
       json (~> 1.4)
+    ref (1.0.5)
     remotipart (1.0.5)
     ri_cal (0.8.8)
     rspec (2.11.0)
@@ -240,7 +242,7 @@ GEM
       railties (>= 3.0)
       rspec (~> 2.11.0)
     rubyzip (0.9.9)
-    safe_yaml (0.9.2)
+    safe_yaml (0.9.3)
     sass (3.2.9)
     sass-rails (3.2.6)
       railties (~> 3.2.0)
@@ -256,6 +258,9 @@ GEM
     sqlite3 (1.3.7)
     themes_for_rails (0.5.1)
       rails (>= 3.0.0)
+    therubyracer (0.11.4)
+      libv8 (~> 3.11.8.12)
+      ref
     thor (0.18.1)
     tilt (1.4.1)
     treetop (1.4.12)
@@ -317,6 +322,7 @@ DEPENDENCIES
   spork (~> 0.9.2)
   sqlite3
   themes_for_rails (= 0.5.1)
+  therubyracer
   validation_reflection!
   warbler
   webrat (= 0.7.3)