Rename `Dydx::Helper#is_num?` to `Dydx::Helper#num?`
Rename `Dydx::Helper#is_0?` to `Dydx::Helper#zero?`
Rename `Dydx::Helper#is_1?` to `Dydx::Helper#one?`
Rename `Dydx::Helper#is_minus1?` to `Dydx::Helper#minus1?`
Merge pull request #30 from gogotanaka/rename_methods

Change method names occurring rubocop CAUTION.