add rvm

see those files and look for `rvm`

+ https://github.com/bhilburn/powerlevel9k/blob/master/CHANGELOG.md
+ https://github.com/bhilburn/powerlevel9k/blob/master/powerlevel9k.zsh-theme

README.md

@@ -129,6 +129,7 @@ The segments that are currently available are:
     * [`chruby`](#chruby) - Ruby environment information using `chruby` (if one is active).
     * [`rbenv`](#rbenv) - Ruby environment information using `rbenv` (if one is active).
     * [`rspec_stats`](#rspec_stats) - Show a ratio of test classes vs code classes for RSpec.
+    * `rvm` - Ruby environment information using `$GEM_HOME` and `$MY_RUBY_HOME` (if one is active).
 * **Rust Segments:**
     * `rust_version` - Display the current rust version and [logo](https://www.rust-lang.org/logos/rust-logo-blk.svg).
 * **Swift Segments:**