Button support global size

examples/main.js

@@ -12,7 +12,8 @@ import locale from '../src/locale/lang/zh-CN';
 Vue.use(VueRouter);
 Vue.use(iView, {
     locale,
-    transfer: true
+    transfer: true,
+    size: 'small'
 });
 
 // 开启debug模式

src/components/button/button.vue

@@ -47,6 +47,9 @@
             size: {
                 validator (value) {
                     return oneOf(value, ['small', 'large', 'default']);
+                },
+                default () {
+                    return this.$IVIEW.size === '' ? 'default' : this.$IVIEW.size;
                 }
             },
             loading: Boolean,