fix(MdDialog): remove md-primary from MdDialogConfirm's cancel button (#1633)

As recommended in #1622

Author: Matt Grande

src/components/MdDialog/MdDialogConfirm/MdDialogConfirm.vue

@@ -4,7 +4,7 @@
     <md-dialog-content v-if="mdContent" v-html="mdContent" />
 
     <md-dialog-actions>
-      <md-button class="md-primary" @click="onCancel">{{ mdCancelText }}</md-button>
+      <md-button @click="onCancel">{{ mdCancelText }}</md-button>
       <md-button class="md-primary" @click="onConfirm">{{ mdConfirmText }}</md-button>
     </md-dialog-actions>
   </md-dialog>