Fix typo

As title

Author: Gusted

options/locale/locale_en-US.ini

@@ -1263,7 +1263,7 @@ issues.filter_sort.moststars = Most stars
 issues.filter_sort.feweststars = Fewest stars
 issues.filter_sort.mostforks = Most forks
 issues.filter_sort.fewestforks = Fewest forks
-issues.keyword_search_unavailable = Currently searhing by keyword is not available. Please contact your site administrator.
+issues.keyword_search_unavailable = Currently searching by keyword is not available. Please contact your site administrator.
 issues.action_open = Open
 issues.action_close = Close
 issues.action_label = Label