Update scratch-vm to pull in changes from scratch-sb1-converter

package.json

@@ -110,7 +110,7 @@
     "scratch-render": "0.1.0-prerelease.20181220195236",
     "scratch-storage": "1.2.2",
     "scratch-svg-renderer": "0.2.0-prerelease.20181220183040",
-    "scratch-vm": "0.2.0-prerelease.20181221030743",
+    "scratch-vm": "0.2.0-prerelease.20181221194157",
     "selenium-webdriver": "3.6.0",
     "startaudiocontext": "1.2.1",
     "style-loader": "^0.23.0",