Remove references to Travis

Summary:
react-native project is migrated travis to circleCI.
but the document has some leavings.

Only Docs Edited

facebook/react-native#16354
facebook/react-native#16364

[ DOCS] Remove references to Travis
changed Releases.md
changed RNTester/RNTesterIntegrationTests/RNTesterSnapshotTests.m
changed scripts/android-e2e-test.js
Closes facebook/react-native#17733

Differential Revision: D6806336

Pulled By: shergin

fbshipit-source-id: 22d21995d718a89bb831f75ed2ff6074dd22c6fe

Author: philographer

RNTesterIntegrationTests/RNTesterSnapshotTests.m

@@ -48,7 +48,6 @@ - (void)test##name                      \
 // No switch or slider available on tvOS
 RCT_TEST(SwitchExample)
 RCT_TEST(SliderExample)
-// TabBarExample on tvOS passes locally but not on Travis
 RCT_TEST(TabBarExample)
 #endif