Merge branch 'dev' into alpha

src/core/view/components/canvas/index.vue

 <template>
-  <uni-canvas
-    :canvas-id="canvasId"
-    :disable-scroll="disableScroll"
+  <uni-canvas
+    :canvas-id="canvasId"
+    :disable-scroll="disableScroll"
     v-on="_listeners">
-    <canvas
-      ref="canvas"
-      width="300"
+    <canvas
+      ref="canvas"
+      width="300"
       height="150" />
     <div style="position: absolute; top: 0; left: 0; width: 100%; height: 100%; overflow: hidden;">
       <slot />
     </div>
-    <v-uni-resize-sensor
-      ref="sensor"
+    <v-uni-resize-sensor
+      ref="sensor"
       @resize="_resize" />
   </uni-canvas>
 </template>
@@ -425,6 +425,7 @@ export default {
         context.drawImageByCanvas(canvas, x, y, width, height, 0, 0, destWidth, destHeight, false)
         imgData = context.getImageData(0, 0, destWidth, destHeight)
         newCanvas.height = newCanvas.width = 0
+        context.__hidpi__ = false
       } catch (error) {
         if (!callbackId) {
           return