fix: fix half screen dialog buttons. close #158

Author: Tidyzq

src/half-screen-dialog/half-screen-dialog.less

@@ -20,4 +20,8 @@
   .weui-half-screen-dialog {
     transform: translateY(0%);
   }
-}
+}
+
+.weui-half-screen-dialog__ft {
+  display: flex;
+}

tools/demo/example/half-screen-dialog/half-screen-dialog.wxml

@@ -12,24 +12,20 @@
         <mp-halfScreenDialog show="{{typeF}}">
           <view slot="title">测试标题A</view>
           <view slot="desc">这是自定义描述区</view>
-          <view slot="footer">
-            <button type="default" class="weui-btn">按钮A</button>
-            <button type="primary" class="weui-btn">按钮B</button>
-          </view>
+          <button slot="footer" type="default" class="weui-btn">按钮A</button>
+          <button slot="footer" type="primary" class="weui-btn">按钮B</button>
         </mp-halfScreenDialog>
         <mp-halfScreenDialog show="{{typeT}}" closabled="{{false}}">
           <view slot="title">测试标题A</view>
           <view slot="desc">这是自定义描述区</view>
-          <view slot="footer">
-            <button type="default" class="weui-btn">按钮A</button>
-            <button type="primary" class="weui-btn">按钮B</button>
-          </view>
+          <button slot="footer" type="default" class="weui-btn">按钮A</button>
+          <button slot="footer" type="primary" class="weui-btn">按钮B</button>
         </mp-halfScreenDialog>
-        <mp-halfScreenDialog 
+        <mp-halfScreenDialog
           bindbuttontap="buttontap"
           show="{{typeS}}"
-          maskClosable="{{false}}" 
-          title="测试标题B" 
+          maskClosable="{{false}}"
+          title="测试标题B"
           subTitle="测试标题B的副标题"
           desc="辅助描述内容，可根据实际需要安排"
           tips="辅助提示内容，可根据实际需要安排"