Don't put spaces around `=` in methods definitions

Just like PEP8: http://www.python.org/dev/peps/pep-0008/#other-recommendations

But it's debatable because it's basically an exception to the rule, and the main ruby style guide disagree: https://github.com/bbatsov/ruby-style-guide

WDYT ?
Convention nazi compliance
Merge pull request #4 from Planbox/default-arguments

Don't put spaces around `=` in methods definitions