Created by: reyoung

• The $TRAVIS_COMMIT_RANGE could not exist, because the git history can be changed and rebased. Here we alway run Travis-CI when git diff cannot return the modified files.

• Also do not push docs update if current Travis-CI is not PaddlePaddle/Paddle.

  • SSL_KEY environment variable is only defined in PaddlePaddle/Paddle Travis-CI environment, and used for push documentation updates.