Update Rails from 5.1.3 to 5.1.6.1

Broken Access Control vulnerability in Active Job
There is a vulnerability in Active Job. This vulnerability has been assigned the CVE identifier CVE-2018-16476.

Patched versions: >= 4.2.11, < 5.0.0; >= 5.0.7.1, < 5.1.0; >= 5.1.6.1, < 5.2.0; >= 5.2.1.1
Unaffected versions: < 4.2.0

How to test: It's Rails, which is everything, but it's a patch version bump. A quick sanity check on posting and browsing should be enough.