feat(rvm): add alias `rvms` (#10219)

* feat(rvm): add alias `rvms`

* docs(rvm): new alias `rvms`

plugins/rvm/README.md

@@ -18,3 +18,4 @@ plugins=(... rvm)
 | `rb21`         | `rvm use ruby-2.1.2` |
 | `rvm-update`   | `rvm get head`       |
 | `gems`         | `gem list`           |
+| `rvms`         | `rvm gemset`         |

plugins/rvm/rvm.plugin.zsh

@@ -1,7 +1,8 @@
 fpath=($rvm_path/scripts/zsh/Completion $fpath)
 
 alias rubies='rvm list rubies'
-alias gemsets='rvm gemset list'
+alias rvms='rvm gemset'
+alias gemsets='rvms list'
 
 local ruby18='ruby-1.8.7'
 local ruby19='ruby-1.9.3'