[ChromeDriver] Fix an error in test_expectation

Adding a comma at the end of the newly added entry

Change-Id: I3d3fb4f86fbedea46489737abb602321f07a67dc
Reviewed-on: https://chromium-review.googlesource.com/1227189Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Artur Khachatryan <khachatryan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591437}

chrome/test/chromedriver/test/test_expectations

@@ -17,7 +17,7 @@ _REVISION_NEGATIVE_FILTER['HEAD'] = [
 
     # https://bugs.chromium.org/p/chromedriver/issues/detail?id=2532
     'SlowLoadingPageTest.testRefreshShouldBlockUntilPageLoads',
-    'PageLoadingTest.testShouldTimeoutIfAPageTakesTooLongToRefresh'
+    'PageLoadingTest.testShouldTimeoutIfAPageTakesTooLongToRefresh',
 
     # https://bugs.chromium.org/p/chromedriver/issues/detail?id=2572
     'ChromeOptionsFunctionalTest.canAddExtensionFromFile',