Fix always displaying system ruby when set by asdf

Since the asdf-ruby integration with bobthefish was written, asdf has changed their ruby version provenance format.
`asdf current ruby 2>/dev/null | read -l asdf_ruby_version asdf_provenance` now results in $asdf_provenance being "   (set by $HOME/.tool-versions)", which results in the system ruby version always being displayed, which is annoying. This is a small patch to fix that. I've tested it locally.

fish_prompt.fish

@@ -781,7 +781,7 @@ function __bobthefish_prompt_rubies -S -d 'Display current Ruby information'
         or return
 
         # If asdf changes their ruby version provenance format, update this to match
-        [ "$asdf_provenance" = "(set by $HOME/.tool-versions)" ]
+        [ "$asdf_provenance" = "   (set by $HOME/.tool-versions)" ]
         and return
 
         set ruby_version $asdf_ruby_version