Removed extra word in test case description.

Differential Revision: https://phabricator.services.mozilla.com/D46276

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1497007
gecko-commit: 91824287186642eaeb94121c51ca39a0f1094625
gecko-integration-branch: autoland
gecko-reviewers: ttung, asuth

Author: sigiesec

IndexedDB/idb-explicit-commit.any.js

@@ -288,5 +288,5 @@ promise_test(async testCase => {
   assert_equals(getRequest1.result.title, 'title1');
   assert_equals(getRequest2.result.title, 'title2');
   db.close();
-}, 'Transactions that handle all errors properly should be behave as ' +
+}, 'Transactions that handle all errors properly should behave as ' +
    'expected when an explicit commit is called in an onerror handler.');