Omit functions and builtins when looking for ruby environment managers

This is especially important for asdf, because it turns out lots of people have aliases and functions called that :)

Fixes #160

fish_prompt.fish

@@ -638,9 +638,9 @@ function __bobthefish_prompt_rubies -S -d 'Display current Ruby information'
   [ "$theme_display_ruby" = 'no' ]; and return
 
   set -l ruby_version
-  if type -q rvm-prompt
+  if type -fq rvm-prompt
     set ruby_version (__bobthefish_rvm_info)
-  else if type -q rbenv
+  else if type -fq rbenv
     set ruby_version (rbenv version-name)
     # Don't show global ruby version...
     set -q RBENV_ROOT
@@ -653,9 +653,9 @@ function __bobthefish_prompt_rubies -S -d 'Display current Ruby information'
       or set -l global_ruby_version system
 
     [ "$ruby_version" = "$global_ruby_version" ]; and return
-  else if type -q chruby
+  else if type -q chruby # chruby is implemented as a function, so omitting the -f is intentional
     set ruby_version $RUBY_VERSION
-  else if type -q asdf
+  else if type -fq asdf
     asdf current ruby 2>/dev/null | read -l asdf_ruby_version asdf_provenance
       or return