Escape singlequotes in fish_completer

In case the completion string has any singlequotes,
escape them before passing it to external fish command.
Else the completion will fail due to unmatched quotes.

eg. vim '/home <tab>

Author: scarlet-storm

cookbook/external_completers.md

@@ -20,7 +20,7 @@ This completer will use [the fish shell](https://fishshell.com/) to handle compl
 
 ```nu
 let fish_completer = {|spans|
-    fish --command $"complete '--do-complete=($spans | str join ' ')'"
+    fish --command $"complete '--do-complete=($spans | str replace "'" "\\'" | str join ' ')'"
     | from tsv --flexible --noheaders --no-infer
     | rename value description
     | update value {