key option added for locations command in test

Author: abdulsuhail

test/fixtures/command-line/help-locations.txt

@@ -4,4 +4,7 @@ list locations and the number of pending tests
 
 Options:
   -e, --request <id>  echo request ID, useful to track asynchronous requests
+  -k, --key <api_key>                 API key (if assigned). Contact the
+                                      WebPageTest server administrator for a
+                                      key if required
   -h, --help          display help for command