Nunjucks: Switch from JSHint to ESLint

[ricordisamoa]

Some of the options currently used by Nunjucks in .jshintrc, e.g. quotmark, have been deprecated by JSHint because they don't concern code correctness. We should maybe have a look at JSCS which is specifically targeted towards code style issues. At first glance, "yandex" seems to be the builtin preset with the fewest errors but a custom one can be easily crafted.

[jgerigmeyer]

If we're making a change, I'd seriously consider ESLint instead of combining JSCS and JSHint.

[carljm]

Yeah, I'd probably also prefer switching to ESLint, which does both in a single tool.

[ricordisamoa]

Given that consensus is clear, and most importantly since most of the JSCS maintainers will join the ESLint team, I am going to update the title.

[fdintino]

This will be fixed by #1052

[fdintino]

Fixed by #1052