changed rspec method names to remove deprecation warnings

[barelyknown]

This fixes these deprecation warnings:

Deprecation Warnings:

`failure_message_for_should_not` is deprecated. Use `failure_message_when_negated` instead. Called from /Users/seandevine/Projects/federatedfreightways/equivalent-xml/lib/equivalent-xml/rspec_matchers.rb:57:in `block in <module:RSpecMatchers>'.

`failure_message_for_should` is deprecated. Use `failure_message` instead. Called from /Users/seandevine/Projects/federatedfreightways/equivalent-xml/lib/equivalent-xml/rspec_matchers.rb:53:in `block in <module:RSpecMatchers>'.

[Eric-Guo]

just I want to commit :smile:

[mbklein]

@barelyknown Thanks for the PR! I would like equivalent-xml's matchers to continue to work with RSpec 2.x, though, so I won't be able to pull and release this change until I get a chance to make a backward-compatible fix. If you come up with one in the meantime and add it to this PR, I'd be happy to pull at that point.

[dpehrson]

Just wanted to pop in here and say I just saw this in my RSpec 3 project when I added the lib.

[DanielHeath]

Fair point - would it make sense to detect the rspec version & use the right method? Otherwise, once they are deprecated equivalent-xml will be broken for users running recent versions.

[barelyknown]

I aliased the old style Rspec methods to the new ones to preserve backwards compatability.

[DanielHeath]

That could cause some very confusing errors for those trying to upgrade (tests pass if equivalent-xml matchers is loaded & fail with an unrelated message otherwise)...

[mbklein]

Yeah, I don't think I'm comfortable reaching into rspec and mucking with its methods. I have an idea on a good middle ground for this; I just need the time to implement it.

[mbklein]

I fixed the deprecation warnings in a backward-compatible, non-invasive way with #23. Thanks for your help and input, everyone!