feat(button): md-icon-button to use round ripple

Author: matthewrfindley

src/components/button/button-theme.scss

@@ -1,5 +1,6 @@
 $button-border-radius: 3px !default;
 $button-fab-border-radius: 50% !default;
+$button-icon-border-radius: $button-fab-border-radius;
 
 a.md-button.md-THEME_NAME-theme,
 .md-button.md-THEME_NAME-theme {
@@ -34,6 +35,10 @@ a.md-button.md-THEME_NAME-theme,
     }
   }
 
+  &.md-icon-button {
+    border-radius: $button-icon-border-radius;
+  }
+
   &.md-primary {
     color: '{{primary-color}}';
     &.md-raised,