Bug 1571567 - Fix no-fallthrough errors in /testing. r=jmaher

Differential Revision: https://phabricator.services.mozilla.com/D40879

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

testing/specialpowers/content/SpecialPowersParent.jsm

@@ -53,6 +53,7 @@ class SpecialPowersParent extends SpecialPowersAPIParent {
               },
               type: permission.type,
             };
+          // fall through
           default:
             this._self.sendAsyncMessage("specialpowers-" + aTopic, msg);
         }