Update dependency acorn to v6.1.1 (#146)

Author: renovate-bot

package.json

@@ -27,7 +27,7 @@
     "rollup": ">= 0.67.4"
   },
   "dependencies": {
-    "acorn": "6.0.5",
+    "acorn": "6.1.1",
     "acorn-dynamic-import": "4.0.0",
     "acorn-walk": "6.1.1",
     "google-closure-compiler": "20190121.0.0",