Bug 1330227 - Skip xpcshell test_update.js on linux, for intermittent failures; r=me,test-only

toolkit/mozapps/extensions/test/xpcshell/xpcshell-shared.ini

@@ -283,8 +283,8 @@ fail-if = os == "android"
 skip-if = os == "win" # Bug 1358846
 [test_uninstall.js]
 [test_update.js]
-# Bug 676992: test consistently hangs on Android
+# Bug 676992: test consistently hangs on Android; bug 1330227 - linux
-skip-if = os == "android"
+skip-if = os == "android" || os == "linux"
 [test_update_webextensions.js]
 tags = webextensions
 [test_updateCancel.js]