add future parser to travis matrix
fix unit testing of limits class

To be consistent with the change in aea2a0f7b0a5935edd92c11984ca163acff3fb7c
fix rspec `be_false` deprecation warning

    Deprecation Warnings:

    `be_false` is deprecated. Use `be_falsey` (for Ruby's conditional semantics) or `be false` (for exact `== false` equality) instead.
fix linter warnings
Merge pull request #2 from jhoblitt/feature/future_parser

Feature/future parser