fix(Message): 修复 l-image-class 外部样式类不生效的问题

close #1270

Author: juzi214032

src/message/index.js

@@ -4,7 +4,7 @@ import validator from '../behaviors/validator';
 
 Component({
   behaviors: [zIndex, watchShow, validator],
-  externalClasses: ['l-class', 'l-image-class'],
+  externalClasses: ['l-class', 'l-image-class','l-class-image'],
   properties: {
     show: Boolean,
     icon: String,

src/message/index.wxml

@@ -3,7 +3,7 @@
     <view style="margin-right:15rpx">
       <l-icon name="{{icon?icon:type}}" size="{{iconSize}}" color="{{type==='warning'?'#333':iconColor}}" />
     </view>
-    <image wx:if="{{image}}" src="{{image}}" class="l-message-image l-class-image"/>
+    <image wx:if="{{image}}" src="{{image}}" class="l-message-image l-class-image l-image-class"/>
     {{content}}
     <slot />
   </block>