[Search History] fix unquoted regex in preview command

Resolves #314. The problem was that the regex used to generate the
preview was unquoted so fish interpreted it as a filename glob. I
also fixed another potential bug by delinating the string replace
command options from its arguments with --.

functions/_fzf_search_history.fish

@@ -23,7 +23,7 @@ function _fzf_search_history --description "Search command history. Replace the
             --scheme=history \
             --prompt="Search History> " \
             --query=(commandline) \
-            --preview="string replace --regex $time_prefix_regex '' {} | fish_indent --ansi" \
+            --preview="string replace --regex '$time_prefix_regex' '' -- {} | fish_indent --ansi" \
             --preview-window="bottom:3:wrap" \
             $fzf_history_opts |
         string split0 |