Remove Deprecated Code

[kmwhite]

When running code in a test suite, it would throw the following warning
messages:

Deprecation Warnings:

`failure_message_for_should_not` is deprecated. Use
`failure_message_when_negated` instead. Called from
lib/testing/rspec.rb:98:in `block in <top (required)>'.

`failure_message_for_should` is deprecated. Use
`failure_message` instead. Called from
lib/testing/rspec.rb:90:in `block in <top (required)>'.

If you need more of the backtrace for any of these deprecations to
identify where to make the necessary changes, you can configure
`config.raise_errors_for_deprecations!`, and it will turn the
deprecation warnings into errors, giving you the full backtrace.

2 deprecation warnings total

This change adopts the newer, generic DSL for writing RSpec matchers.

When testing these changes, they came back all green, but the file spec/dummy/db/schema.rb had been changed. Reviewing those changes, it showed that all the force: true settings in the table declarations had been changed to force: :cascade. I did not include that file in this PR as I'm unsure if the source of it was a specific thing in Rails or my setup. I'm more happy to include that diff if desired.

[kmwhite]

This request would supersede PR #7 as it corrects more deprecated lines than #7 has and passed specs.

[albertosaurus]

@kmwhite You have a newer version of rails than my dev version, I think. What would be the minimum version of RSpec where this would work?

[kmwhite]

@albertosaurus Apologies for the delays -- work had me all over the place. It looks like rspec-expectations, version 3.0.0beta2 introduced this new syntax.