Make tests more resilient to updates in vulnerability data.

This should cause tests to fail when the format changes, but prevent
failures simply because a previously-not-known-to-be-vulnerable
version had a vulnerability discovered in it.

The caveat is that the `secure` bundle will still kvetch when one of
its gems comes up vulnerable, since it's expected to have ZERO
matches.  In that case, the relevant Gemfile/Gemfile.lock need to be
updated.
Update the secure bundle to reference versions that don't have known vulns.
DRY up a bit.

While this code is more complex, it doesn't duplicate logic from
Bundler::Audit::Advisory.
Improve .gitignore a bit.
Test a particular failure mode that was not previously covered.

Specifically, what happens when `Advisory` is handed YAML that's
structurally mismatched to its' expectations.
Add Ruby 2.0.0 to Travis tests.
Just be clear in the README that there's a constraint on the RubyGems version.

In practice this should be a non-issue, but for the sake of thoroughness I
think it's worth including.
Merge pull request #57 from MrJoy/make_readme_more_precise

Just be clear in the README that there's a constraint on the RubyGems version.
Merge pull request #55 from MrJoy/gitignore_touchups

Improve .gitignore a bit.
Merge pull request #54 from MrJoy/broaden_tests_a_bit

Broaden tests a bit
Merge pull request #51 from MrJoy/database_test_coverage

Test coverage for the Database class.
Merge pull request #52 from MrJoy/make_tests_more_resilient2

Make tests more resilient to changes in details of the output from `bundler-audit`.
Started updating the ChangeLog for 0.3.1.
Style.
Updated ruby-advisory-db
Added rake task and tests
Invoke Thor CLI in this ruby process. Instead of duplicating code and having output consistent, call the Thor check command for now. Keeping this simple
Merge pull request #64 from dekz/rake_task

Added rake task and tests
Use ENV['HOME'] so we can override HOME.
Convert all say messages to Strings (closes #65).

* Bundler 1.5.0 updated their vendored version of Thor, which now
  expects all messages pass to #say be Strings.