typo fix

Author: krichprollsch

src/tests/html/script/importmap.html

@@ -15,7 +15,7 @@
   testing.expectEqual('hello', im.greeting);
 </script>
 
-<script id=cached_importmpa type=module>
+<script id=cached_importmap type=module>
   // hopefully cached, who knows, no real way to assert this
   // but at least it works.
   import * as im from 'core';