WIP on Rails 5.0 compat

[Epigene]

Hello, John,

Here I've started to make the gem compatible with Rails v5.0, the main idea is to bump Ruby version and refactor alias_method_chain to Module#prepend use.

Unfortunately, I ran into a weird problem - running rspec errs out:

NameError:
  uninitialized constant ActionView::Helpers::InstanceTag
# ./lib/validates_timeliness/extensions.rb:9:in `enable_date_time_select_extension!'

The thing is, when I check out my Rails 5.0-using app the constant is defined, so not sure what is going on. I also tried require 'rails' to see if maybe require namespace has changed, but no, still undefined.

Maybe you have an idea how I could proceed.

[coveralls]

Coverage decreased (-46.05%) to 49.749% when pulling 0c64aa0 on Epigene:rails5-compat into 9e5e8f8 on johncarney:master.