title: localStorage is not defined when call to tokenNotExpired
body: <p>i want to integrate angular2-jwt in my project : <a href="https://github.com/auth0/angular2-jwt" rel="nofollow noreferrer">https://github.com/auth0/angular2-jwt</a></p>
  
  <p>when i try to call the function tokenNotExpired i get this exception :</p>
  
  <blockquote>
    <p>Exception: Call to Node module failed with error: ReferenceError:
    localStorage is not defined at Object.tokenNotExpired</p>
  </blockquote>
  
  <p>this is my code :</p>
  
  <p><strong><em>auth.service.ts</em></strong></p>
  
  <pre><code>import { Injectable } from '@angular/core';
  import { tokenNotExpired } from 'angular2-jwt';
  
  @Injectable()
  export class Auth {
  
      loggedIn() {
          return tokenNotExpired();
      }
  
  }
  </code></pre>
  
  <p><strong><em>app.component.ts</em></strong></p>
  
  <pre><code>import { Component } from '@angular/core';
  import { Auth } from '../.././services/auth.service';
  
  @Component({
      selector: 'app',
      templateUrl: './app.component.html',
      styleUrls: ['./app.component.css']
  })
  export class AppComponent {
      constructor(private auth: Auth) { }
  }
  </code></pre>
  
  <p><strong><em>app.component.html</em></strong></p>
  
  <pre><code>&lt;div class='container-fluid'&gt;
      &lt;div class='row'&gt;
          &lt;div *ngIf="auth.loggedIn()" class='col-sm-3'&gt;
              &lt;nav-menu&gt;&lt;/nav-menu&gt;
          &lt;/div&gt;
          &lt;div class='col-sm-9 body-content'&gt;
              &lt;router-outlet&gt;&lt;/router-outlet&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Thanks</p>