Update dependency acorn to v5.7.2 (#43)

Author: renovate[bot]

package-lock.json

@@ -27,7 +27,7 @@
     "rollup": ">= 0.63.5"
   },
   "dependencies": {
-    "acorn": "5.7.1",
+    "acorn": "5.7.2",
     "google-closure-compiler": "20180805.0.0",
     "magic-string": "0.25.0",
     "temp-write": "3.4.0"