Added - alias of rm

Readme.md

@@ -34,6 +34,10 @@ Remove some versions:
 
     $ n rm 0.2.4 0.3.0
 
+Instead of using `rm` we can simply use `-`:
+
+    $ n - 0.2.4
+
 ## Usage
 
  Output from `n --help`:

bin/n

@@ -180,7 +180,7 @@ else
     case $1 in
       -V|--version) display_n_version ;;
       -h|--help) display_help ;;
-      rm) shift; remove_version $@; exit ;;
+      rm|-) shift; remove_version $@; exit ;;
       *) install_node $@; exit ;;
     esac
     shift