Update latest version in README (#100)

Author: koddsson

README.md

@@ -30,7 +30,7 @@ Currently handles
 Add this line to your application's Gemfile:
 
 ```ruby
-gem "w_syntax_tree-erb", "~> 0.11", require: false
+gem "w_syntax_tree-erb", "~> 0.12", require: false
 ```
 
 > I added the `w_` prefix to avoid conflicts if there will ever be an official `syntax_tree-erb` gem.