This is now done by `brew test-bot`.

This ins stored in vendor/bundle now instead.

- Update Xcode version
- Split out platform-specific code so we can see where time is spent
- Manually trigger vendor Ruby installation
- Use `brew update` to update things
- Use `travis_retry` where relevant.

Rearrange the test-bot clones so that the Homebrew/homebrew-core move
can be successful to avoid the later clone.

Use this version whenever 2.3.3 isn't installed. Also, remove the Linux
portable Ruby for now until it's built to be the same version.

Change the umask before we create any files to avoid `brew audit`
complaining about the `chmod` of formulae.

This avoid two weird things:

- scary messages when building tags fails
- two builds being run instead of one when people create a PR and a
  branch on the Homebrew/brew repo (rather than their fork).

Show failing Linux builds (which run much more quickly) before the macOS
build has completed.

https://docs.travis-ci.com/user/customizing-the-build/#Fast-Finishing

To match https://github.com/Homebrew/homebrew-test-bot/pull/112.

On Linux this is currently blowing up for our tags so let's change the
approach.

Remove `testbottest` formula (this should have lived in the `brew
test-bot` repository from the outset) and make various other changes to
fix the Linux build here.

This requires updating to Rubocop 0.49.0 which will require some fixes
to rules, in Homebrew/brew and Homebrew/homebrew-core but opening this
for now so I remember.

Attempt to improve Travis CI. This time without any vendoring gems
nonsense.

This reverts commit 3e4547f5, reversing
changes made to 6edf9382.

This reverts commit 8d948e4b, reversing
changes made to 23728729.

Tweak our Travis CI configuration and the one we suggest for taps to
be faster and use caching.

Homebrew's actually ended up using a fair few gems. While we want to
avoid Bundler at runtime (and this PR still does that, in fact uses
Bundler even less at runtime than it did before) writing our own version
to use at build-time seems redundant.

Travis needs some coaxing to find where we put it. This should improve
build reliability due to network issues.

This will avoid `brew doctor` trying to retap `homebrew/core` which is
both slow and error-prone.

For code coverage from `brew test-bot`.

OS X Travis CI is particularly error-prone, slow and unnecessary for
us when we're already running (fast) OS X builds on Jenkins so use it
just for Linux testing.

This should verify that we're not breaking our tests on Linux.

We have Jenkins to test the other versions.

Putting the Ruby 1.8 we use to run tests on 10.9 into the PATH adversely
affects formulae with a Ruby dependency (possibly other formulae, too).
Remove this hack, as it is no longer needed.

Closes Homebrew/homebrew#47694.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Closes Homebrew/homebrew#43635.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Closes Homebrew/homebrew#47056.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>