Re-enable import/no-duplicates for eslint once it supports import type

[noahbrenner]

Since import type ... is a recent addition to TypeScript, it's not yet supported by the import/no-duplicates eslint rule. This means that the following is currently reported as an error due to having multiple imports from the same package, even though one of the lines only imports types:

import {foo} from 'foo';
import type {FooType} from 'foo';

The rule already supports similar syntax for flow and there is an existing issue requesting the same support for Typescript: import-js/eslint-plugin-import#1667

In order to make use of the import type syntax, we had to temporarily disable this rule.

Once TypeScript import type support is added, we should re-enable the import/no-duplicates rule.

[noahbrenner]

This was fixed in #12