Fix build break from macOS - Auth merge (#59)

Author: paulb777

Example/Auth/Tests/FIRAuthTests.m

@@ -1215,7 +1215,7 @@ - (void)testCreateUserEmptyEmailFailure {
   XCTestExpectation *expectation = [self expectationWithDescription:@"callback"];
   [[FIRAuth auth] signOut:NULL];
   [[FIRAuth auth] createUserWithEmail:@""
-                             password:kPassword
+                             password:kFakePassword
                            completion:^(FIRUser *_Nullable user, NSError *_Nullable error) {
     XCTAssertTrue([NSThread isMainThread]);
     XCTAssertEqual(error.code, FIRAuthErrorCodeMissingEmail);