Fix Travis-ci builds (#950)
Fix Travis-ci builds (#950)

Line "- /usr/local/bin:$PATH" is misformatted.
It must be something like "- PATH=/usr/local/bin:$PATH".

It seems something changed in tarvis-ci month ago and now this leads to:

Setting environment variables from .travis.yml
$ export PATH=

Defailt PATH is /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin
so already containts /usr/local/bin.


Image "xcode8.3" contains macOS 10.12 (sierra) which has no bottles
with precompiled gcc-7 in homebrew storage.

Image "xcode9.4" is a current default with macOS 10.13 (high_sierra).

Link: https://docs.travis-ci.com/user/reference/osx/
Link: 77b40ace499f4dfe0163bca8a35ce7f5a3a52d20@7

Signed-off-by: Konstantin Khlebnikov <3b96b99f19643d33e1bfa1caa535c041c3608549@yandex-team.ru>

mockingbirdnest/benchmark,google/benchmark,google/benchmark,mockingbirdnest/benchmark,mockingbirdnest/benchmark,mockingbirdnest/benchmark,google/benchmark