CI integration does not run check-boilerplate.sh

https://github.com/GoogleCloudPlatform/PerfKitBenchmarker/pull/1386 got a pass from Travis CI
https://travis-ci.org/GoogleCloudPlatform/PerfKitBenchmarker/jobs/236219931 even though running hooks/check-everything from a repo fails with
```
*** ERROR: *** Some files are missing the required boilerplate
header from hooks/lib/boilerplate.*.txt:
perfkitbenchmarker/linux_benchmarks/ch_block_storage_benchmark.py
perfkitbenchmarker/linux_packages/ch_block_storage.py
perfkitbenchmarker/linux_packages/php.py
See hooks/boilerplate.*.txt for required headers.
```
Travis CI should run the same tests as check/everything.