fix travis test

Author: sllethe

src/lib/list/selection-list.spec.ts

@@ -1,5 +1,5 @@
 import {async, TestBed, ComponentFixture, inject} from '@angular/core/testing';
-import {Component, DebugElement, ViewChildren} from '@angular/core';
+import {Component, DebugElement} from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {MdSelectionList, MdListOption, MdListModule} from './index';
 import {createKeyboardEvent} from '@angular/cdk/testing';