Update matchers for RSpec 3.0

Set gemspec to use RSpec 2.99
Add `supports_block_expectations` to Reactor's supplied test matchers
Remove unnecessary `with` with no arguments

Convert specs using `transpec`
For more details: https://github.com/yujinakayama/transpec#supported-conversions
Merge pull request #16 from hired/rspec-2.99

Upgrade to RSpec 2.99.x