update contributing docs with rbenv instructions

CONTRIBUTING.md

@@ -22,33 +22,41 @@ grunt test build
 
 #### Development Environment Setup
 
-- install node.js (we recommend using [nvm](https://github.com/creationix/nvm))
+- Install node.js (we recommend using [nvm](https://github.com/creationix/nvm))
 
   ```sh
   ## follow directions at https://github.com/creationix/nvm, then
   nvm install 0.10
   ```
 
-- install ruby (we recommend using [rvm](http://rvm.io/rvm/install), which also installs the `bundler` gem that is required later)
+- Install ruby *1.9.3-p547* (we recommend using [rbenv](https://github.com/sstephenson/rbenv))
+  - See [rbenv docs](https://github.com/sstephenson/rbenv#installation) for installation assistance
 
   ```sh
-  ## follow directions at http://rvm.io/rvm/install, then
-  rvm install 1.9
+  ## install ruby and ruby-build using your local package manager (apt, brew, etc)
+  ## ex. brew install rbenv ruby-build
+  - Run `rbenv init` and add `eval "$(rbenv init -)"` to your shell (ex. .bashrc/.bash_profile)
+  - Run `rbenv install 1.9.3-p547` to install the required version
+  - Run `ruby -v` and make sure you are using 1.9.3-p547
+    - If not, run `rbenv global 1.9.3-p547` and check again
+    - Check the installation docs if you continue to have issues
+  - Install bundler by running `gem install bundler`
+  - Install local gems by running `cd src/server; bundle; cd ../..`
   ```
 
-- install grunt and bower globally
+- Install grunt and bower globally
 
   ```sh
   npm install -g grunt-cli bower
   ```
 
-- install node, bower, and ruby dependencies
+- Install node, bower, and ruby dependencies
 
   ```sh
   npm install && bower install && cd src/server && bundle && cd ../..
   ```
 
-- start the development server.
+- Start the development server.
 
   ```sh
   grunt dev # use the "--with-es" flag to install & start elasticsearch too