RS-4458 require ruby 2.5

[jeffbax]

Leaving .ruby-version and the rails app to require 2.5.8 specifically for now... I was tempted to do 2.6.6 (specs passed) but ruby 2.6.x is not mentioned until Rails 5.2

Otherwise:

• fixes missed rspec deprecations
• adds some UI credits given our hacking it up at this point
• drops rails < 4.2.10 (because why not)

[rsaris]

We likely can remove the support for pre Rails 4 strong params in the models but that's a bit to unpack today and isn't technically necessary for this.

[rsaris]

Will this stop us from patching this if needed? Is there any reason to require 2.5 vs. just setting this repo to use it and assuming it supports it?

[jeffbax]

Well, there are actual test breakages between 2.4 and 2.5 from the CSV library, so its a bit of a line in the sand.

In either case, I have the rails app ready for 2.5 already and tested happy path