Update stuff regarding no-tabs

[lydell]

ESLint 5.7 added the allowIndentationTabs option. This might turn the rule from a special rule to a validatable one.

https://eslint.org/blog/2018/10/eslint-v5.7.0-released

[lydell]

This might be a breaking change, so we should probably wait for a little while.

[lydell]

Status: Yes, this can be turned into a validatable rule. But that would require bumping the peerDependency on ESLint from >=3.14.1 to >=5.7.0. Since nobody has complained about this and there’s a note about it in the docs, I think it’s better to leave this open at least until ESLint 6 is released, or when enough people have migrated to a new enough ESLint version.