fix docs to reflect how to lint with rubocop

[andrewmcodes]

After running through the issues and spending a few hours trying to figure out why rubocop, I came to the following conclusions:

Rubocop linting works if the settings are as follows:

	"rubocop": {
		"only": ["SpaceInsideBlockBraces", "LeadingCommentSpace"],
		"lint": false,
		"rails": false
	},

or

	"rubocop": {
		"rails": true
	},

I am opening this PR so that others can give input, as I could not find the core issue on my own. But, it looks like if lint: true is not included in the rubocop settings, linting works as expected. This is consistent the behavior described in #261.

• [] The build passes
• TSLint is mostly happy
• Prettier has been run

[javiervidal]

Yes, lint: true does not work inside rubocop.

[wingrunr21]

This shouldn't be needed anymore with #405 merged. It should make the RuboCop linting much more resilient.