tools: Use $PATH to determine location for phantomjs

Another place we want to use $PATH to determine the location of
phantomjs, in case it's installed to a home directory.

Closes #1233
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>

tools/tap-phantom

@@ -1,4 +1,4 @@
-#!/usr/bin/phantomjs
+#!/usr/bin/env phantomjs
 
 /*
  * Copyright (C) 2013 Red Hat, Inc.