Bump acorn from 6.1.1 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.1.1 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.1.1...6.4.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package.json

@@ -15,7 +15,7 @@
     "@babel/core": "^7.2.2",
     "@babel/plugin-syntax-dynamic-import": "^7.2.0",
     "@babel/preset-env": "^7.3.1",
-    "acorn": "^6.0.5",
+    "acorn": "^6.4.1",
     "acorn-dynamic-import": "^4.0.0",
     "autoprefixer": "^9.4.8",
     "babel-loader": "^8.0.5",

yarn.lock

@@ -973,10 +973,10 @@ acorn@^4.0.4, acorn@~4.0.2:
   resolved "https://registry.yarnpkg.com/acorn/-/acorn-4.0.13.tgz#105495ae5361d697bd195c825192e1ad7f253787"
   integrity sha1-EFSVrlNh1pe9GVyCUZLhrX8lN4c=
 
-acorn@^6.0.5:
-  version "6.1.1"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.1.1.tgz#7d25ae05bb8ad1f9b699108e1094ecd7884adc1f"
-  integrity sha512-jPTiwtOxaHNaAPg/dmrJ/beuzLRnXtB0kQPQ8JpotKJgTB6rX6c8mlf315941pyjBSaPg8NHXS9fhP4u17DpGA==
+acorn@^6.0.5, acorn@^6.4.1:
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
+  integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
 ajv-errors@^1.0.0:
   version "1.0.1"