no-unused-variable: ignore-pattern doesn't apply to imports

[brandf]

Bug Report

• TSLint version: ^5.6.0
• TypeScript version: ^2.4.2
• Running TSLint via: (pick one) CLI / Node.js API / VSCode / grunt-tslint / Atom / Visual Studio / etc
  webpack tslint-loadeder and CLI

TypeScript code being linted

import { UI } from '../../ui';

with tslint.json configuration:

"no-unused-variable": [true, {"ignore-pattern": "(^_+$)|(^UI$)"}]

Actual behavior

All imports are unused.

Expected behavior

No error because ignore-pattern matches 'UI'

[ajafff]

Fixed by #3187