Support for standard

[fidalgo]

Since standard (https://github.com/testdouble/standard) uses Rubocop under the wood, it would be nice for ruumba to inherit the rubocop rules from StandardRB.

[ericqweinstein]

Thanks for this! 100% agree; I've mentioned this to Searls and I plan to support Standard soon-ish. (Please feel free to make a pull request if you have time/bandwidth/interest/&c).