doc: Update a typo in module.js' comments

PR-URL: nodejs/node#16205
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>

lib/module.js

@@ -156,7 +156,7 @@ function toRealPath(requestPath) {
   });
 }
 
-// given a path check a the file exists with any of the set extensions
+// given a path, check if the file exists with any of the set extensions
 function tryExtensions(p, exts, isMain) {
   for (var i = 0; i < exts.length; i++) {
     const filename = tryFile(p + exts[i], isMain);