adding the call to the module webcompat#451

Author: karlcow

tests/test_urls.py

@@ -15,6 +15,7 @@
 import webcompat
 
 from webcompat.issues import filter_new
+from webcompat.helpers import format_link_header
 from webcompat.helpers import parse_link_header
 
 # Any request that depends on parsing HTTP Headers (basically anything