General fixes and travis-ci config

this pull request contains:

 * there's no need to have Gemfile.lock in repository, so I've removed and ignored it (via gitignore).
 * fixed failing tests in constants_spec
 * removed unnecessary 'filter_run :focus` config of rspec
 * added travis' config (with this change you can add build status of parsi-date into README file, take a look at https://github.com/everplays/parsi-date/commit/ade5f66970930f7c2278f381807bb88c544a45c1 and [my fork](https://github.com/everplays/parsi-date#readme))