title: Error in importing MatTabChangeEvent
body: <p>I am trying to use the angular material library.
  I have added the dependency for @angular/material in package.json as follows </p>
  
  <pre><code>"@angular/animations": "^5.0.0",
  "@angular/cdk": "^6.0.0",
  "@angular/material": "^5.2.5",
  </code></pre>
  
  <p>When I use </p>
  
  <pre><code>import { MatTabChangeEvent } from '@angular/material';
  </code></pre>
  
  <p>It throws the error while compilation</p>
  
  <pre><code>ERROR in [at-loader] ./node_modules/@angular/material/stepper/typings/stepper.d.ts:28:5
  TS2416: Property '_stepHeader' in type 'MatStepper' is not assignable to the same property in base type 'CdkStepper'.
  Type 'QueryList&lt;ElementRef&gt;' is not assignable to type 'QueryList&lt;FocusableOption&gt;'.
  Type 'ElementRef' is not assignable to type 'FocusableOption'.
    Property 'focus' is missing in type 'ElementRef'.
  </code></pre>
  
  <p>I haven't added any code related to angular material, except that import line.</p>