Add lintTextSync method?

[tunnckoCore]

It's not cool that .lintText requires a callback and ESLint's method is synchronous, but we here force cb for no reason. Or okey, at least add .lintTextSync method?

There is existing problem for https://github.com/dtinth/atom-prettier-standard-formatter, which is based on https://github.com/dtinth/prettier-standard-formatter, which uses promises, exactly because the standards lintText method.

ping @dtinth, stay tuned :)

[feross]

Fair point. There's no need for this to be async. PR here: #157

[tunnckoCore]

cool, thanks

[feross]

FYI, this PR affects the lintText method: #159