fix Relation#merge in Rails 4
fix Relation#merge in Rails 4

it allows hashes. we just don't care about that for switchman

Change-Id: I17192535a4d18fe26260c19a02ccc913db5e560e
Reviewed-on: https://gerrit.instructure.com/41661
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

ccutrer/switchman,krrg/switchman,instructure/switchman,instructure/switchman