Added stackoverflow in /plugins/web-search/-web-search

plugins/web-search/web-search.plugin.zsh

@@ -17,7 +17,7 @@ function web_search() {
     ecosia      "https://www.ecosia.org/search?q="
     goodreads   "https://www.goodreads.com/search?q="
     qwant       "https://www.qwant.com/?q="
-    stackoverflow 'https://stackoverflow.com/search?q="
+    stackoverflow  "https://stackoverflow.com/search?q="
   )
 
   # check whether the search engine is supported