Bug 1497898 - Fix the .gitignore rules, r=ato

Depends on D8228

Differential Revision: https://phabricator.services.mozilla.com/D8229

--HG--
extra : moz-landing-system : lando

testing/web-platform/tests/.gitignore

@@ -5,13 +5,14 @@ _venv/
 .cache/
 .pytest_cache/
 .tox/
+.coverage*
 
 # Node
 node_modules/
 
 # WPT repo stuff
 /MANIFEST.json
-/.wptcache/
+.wptcache/
 /config.json
 
 # Various OS/editor specific files