fish_prompt - __bobthefish_rvm_info: better rvm installation path search method

fish_prompt.fish

@@ -584,12 +584,11 @@ end
 
 function __bobthefish_rvm_info -S -d 'Current Ruby information from RVM'
   # look for rvm install path
-  [ -z "$__rvm_install_path" -a -n "$rvm_path"             ] ; and set -Ux __rvm_install_path "$rvm_path"
-  [ -z "$__rvm_install_path" -a -d /usr/local/rvm          ] ; and set -Ux __rvm_install_path /usr/local/rvm
-  [ -z "$__rvm_install_path" -o ! -d "$__rvm_install_path" ] ; and set -Ux __rvm_install_path ~/.rvm
+  set -q rvm_path
+    or set -l rvm_path ~/.rvm /usr/local/rvm
   
   # More `sed`/`grep`/`cut` magic...
-  set -l __rvm_default_ruby (grep GEM_HOME "$__rvm_install_path"/environments/default | sed -e"s/'//g" | sed -e's/.*\///')
+  set -l __rvm_default_ruby (grep GEM_HOME $rvm_path/environments/default | sed -e"s/'//g" | sed -e's/.*\///')
   set -l __rvm_current_ruby (rvm-prompt i v g)
   [ "$__rvm_default_ruby" = "$__rvm_current_ruby" ]; and return