Store the timestamp of the vendored ruby-advisory-db in a separate file.
Updated ruby-advisory-db
Store the ruby-advisory-db timestamps in UTC.
Begin adding some -- clunky, but functional -- code for testing the Database class more thoroughly.

Note the one test failure is due to a bug in the Database class.
Update vuln DB.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Rakefile
	lib/bundler/audit/database.rb
Merge branch 'database_test_coverage'

Conflicts:
	spec/spec_helper.rb