docs(overview): correct the input validation example

The documentation says that the input should be red if you enter
invalid values or leave it blank. Because the type="integer" is not
supported this does not happen in practice.  This fix changes the
input type to number and adds an ng-pattern to ensure that the number
is an integer.

Author: jaredbeck

docs/content/guide/overview.ngdoc

@@ -90,7 +90,7 @@ concepts which the application developer may face:
       <table>
        <tr><td>Quantity</td><td>Cost</td></tr>
        <tr>
-         <td><input type="integer" min="0" ng-model="qty" required ></td>
+         <td><input type="number" ng-pattern="/\d+/" step="1" min="0" ng-model="qty" required ></td>
          <td><input type="number" ng-model="cost" required ></td>
        </tr>
       </table>
@@ -124,7 +124,7 @@ We load Angular using the  `<script>` tag:
 From the `ng-model` attribute of the `<input>` tags, Angular automatically sets up two-way data
 binding, and we also demonstrate some easy input validation:
 
-    Quantity: <input type="integer" min="0" ng-model="qty" required >
+    Quantity: <input type="number" ng-pattern="/\d+/" step="1" min="0" ng-model="qty" required >
     Cost: <input type="number" ng-model="cost" required >
 
 These input widgets look normal enough, but consider these points: