EmrEtlRunner: bump bundler to 1.16.2

[BenFradet]

Bundler is part of the default gems on travis and has to be reinstalled through hacks (c.f.

snowplow/.travis.yml

Lines 54 to 59 in a1bf092

	- rvm implode --force
	- \curl -sSL https://get.rvm.io | bash -s 1.27.0
	- rvm reload
	- rvm install jruby-9.1.6.0
	- gem uninstall -i /home/travis/.rvm/gems/jruby-9.1.6.0 bundler -a -x
	- gem install bundler -v 1.15.4

and travis-ci/travis-ci#8717).

However, jruby is the only ruby version which remains and so we've had to reinstall a ruby version before deploy in #3689 because of travis-ci/dpl#778.

Once we upgrade bundler, all of this can hopefully be removed.

[BenFradet]

descheduling, bundler on travis is 1.16.0 which doesn't contain the necessary fix.

[peel]

Triage: not needed, bumped to 2.x series in snowplow/emr-etl-runner new home