fix(select): spinner size

Due to the new changes in the `progressCircular` component,
the spinner was being rendered bigger than usual. This change
reverts to the old size.

Fixes #7505. Closes #7506

Author: crisbeto

src/components/select/select.js

@@ -87,9 +87,9 @@ angular.module('material.components.select', [
  * </hljs>
  *
  * At first one might expect that the select should be populated with "Bob" as the selected user. However,
- * this is not true. To determine whether something is selected, 
+ * this is not true. To determine whether something is selected,
  * `ngModelController` is looking at whether `$scope.selectedUser == (any user in $scope.users);`;
- * 
+ *
  * Javascript's `==` operator does not check for deep equality (ie. that all properties
  * on the object are the same), but instead whether the objects are *the same object in memory*.
  * In this case, we have two instances of identical objects, but they exist in memory as unique
@@ -98,7 +98,7 @@ angular.module('material.components.select', [
  * To get around this, `ngModelController` provides a `track by` option that allows us to specify a different
  * expression which will be used for the equality operator. As such, we can update our `html` to
  * make use of this by specifying the `ng-model-options="{trackBy: '$value.id'}"` on the `md-select`
- * element. This converts our equality expression to be 
+ * element. This converts our equality expression to be
  * `$scope.selectedUser.id == (any id in $scope.users.map(function(u) { return u.id; }));`
  * which results in Bob being selected as desired.
  *
@@ -144,7 +144,7 @@ function SelectDirective($mdSelect, $mdUtil, $mdTheming, $mdAria, $compile, $par
         .find('md-content')
         .prepend(angular.element(
           '<div>' +
-          ' <md-progress-circular md-mode="{{progressMode}}" ng-hide="$$loadingAsyncDone"></md-progress-circular>' +
+          ' <md-progress-circular md-mode="{{progressMode}}" ng-hide="$$loadingAsyncDone" md-diameter="25px"></md-progress-circular>' +
           '</div>'
         ));
 
@@ -284,7 +284,7 @@ function SelectDirective($mdSelect, $mdUtil, $mdTheming, $mdAria, $compile, $par
             }
           });
 
-        // Wait until postDigest so that we attach after ngModel's 
+        // Wait until postDigest so that we attach after ngModel's
         // blur listener so we can set untouched.
         $mdUtil.nextTick(function () {
           element.on('blur', function() {