Travis shouldn't fail when clang-format suggests improvements

Summary: This diff avoids failing travis test when clang-format fails. We should keep the test green even if clang-format fails. It would be good to look at travis output for pull requests to make sure they're following the good code style. However, we broke travis test 3 times today because of formatting issues. We should keep travis test green if the only thing wrong is the formatting.

Test Plan: none

Reviewers: sdong, yhchiang, anthony

Reviewed By: anthony

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D48291

.travis.yml

@@ -33,7 +33,7 @@ before_script:
 # Lousy hack to disable use and testing of fallocate, which doesn't behave quite
 # as EnvPosixTest::AllocateTest expects within the Travis OpenVZ environment.
 script:
-  - if [[ "${TRAVIS_OS_NAME}" == 'linux' ]]; then OPT=-DTRAVIS CLANG_FORMAT_DIFF=/tmp/clang-format-diff.py make format; fi
+  - if [[ "${TRAVIS_OS_NAME}" == 'linux' ]]; then OPT=-DTRAVIS CLANG_FORMAT_DIFF=/tmp/clang-format-diff.py make format || true; fi
   - OPT=-DTRAVIS V=1 make -j4 check && OPT=-DTRAVIS V=1 make clean jclean rocksdbjava jtest
 
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