解决IE兼容性问题，降级simple-drawing-board 到1.4.1

package.json

@@ -34,7 +34,7 @@
     "nprogress": "0.2.0",
     "path-to-regexp": "2.4.0",
     "screenfull": "3.3.3",
-    "simple-drawing-board": "^2.0.1",
+    "simple-drawing-board": "1.4.1",
     "vue": "2.5.17",
     "vue-count-to": "1.0.13",
     "vue-router": "3.0.2",