Bug 1479078 - Update webgl-mochitest subsuite to new webgl job name.

Differential Revision: https://phabricator.services.mozilla.com/D2476

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

dom/canvas/test/webgl-mochitest/mochitest.ini

@@ -1,5 +1,5 @@
 [DEFAULT]
-subsuite = webgl
+subsuite = webgl1-core
 
 support-files =
   ensure-exts/ensure-ext.js