fixed typo in registration form

Author: Jason Watmore

app/register/register.component.html

@@ -1,12 +1,12 @@
 <div class="col-md-6 col-md-offset-3">
     <h2>Register</h2>
     <form name="form" (ngSubmit)="f.form.valid && register()" #f="ngForm" novalidate>
-        <div class="form-group" [ngClass]="{ 'has-error': f.submitted && !username.valid }">
+        <div class="form-group" [ngClass]="{ 'has-error': f.submitted && !firstName.valid }">
             <label for="firstName">First Name</label>
             <input type="text" class="form-control" name="firstName" [(ngModel)]="model.firstName" #firstName="ngModel" required />
             <div *ngIf="f.submitted && !firstName.valid" class="help-block">First Name is required</div>
         </div>
-        <div class="form-group" [ngClass]="{ 'has-error': f.submitted && !username.valid }">
+        <div class="form-group" [ngClass]="{ 'has-error': f.submitted && !lastName.valid }">
             <label for="lastName">Last Name</label>
             <input type="text" class="form-control" name="lastName" [(ngModel)]="model.lastName" #lastName="ngModel" required />
             <div *ngIf="f.submitted && !lastName.valid" class="help-block">Last Name is required</div>