Fix formatter issue

[i05nagai]

clang-format formats code differently depending on its version. That causes inconsistent results between the local environment and Travis CI. Here we add a docker image for clang-format and remove the validity check on OSX of Travis CI.

Changes

• We remove the script to check code format on OSX.
  • Behavior of clang-format depends on its version. On OSX with brew, it's a bit difficult to control the version of installed packages. In addition to that, we provide a docker image for formatting code which runs on Linux
• Install buildifier and enable checking Bazel code in Travis CI
  • Fixing Install buildifier in Travis CI environment #14

[coveralls]

Pull Request Test Coverage Report for Build 163

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 88.766%

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Totals
Change from base Build 127:	0.0%
Covered Lines:	561
Relevant Lines:	632

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💛 - Coveralls

[ktpr1223214]

./tools/docker/gcc/docker_build_ubuntu1604.sh
./tools/docker_run_formatter.sh

I run these commands on local machine, and they seem to work quite well. Thanks for fixing this issue.
LGTM!

[i05nagai]

Thanks for the confirmation 😃