Bump acorn from 5.7.3 to 5.7.4

Bumps [acorn](https://github.com/acornjs/acorn) from 5.7.3 to 5.7.4.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@5.7.3...5.7.4)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

yarn.lock

@@ -818,8 +818,9 @@ acorn-walk@^6.0.1:
   resolved "https://registry.npm.taobao.org/acorn-walk/download/acorn-walk-6.2.0.tgz#123cb8f3b84c2171f1f7fb252615b1c78a6b1a8c"
 
 acorn@^5.5.3:
-  version "5.7.3"
-  resolved "https://registry.npm.taobao.org/acorn/download/acorn-5.7.3.tgz?cache=0&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Facorn%2Fdownload%2Facorn-5.7.3.tgz#67aa231bf8812974b85235a96771eb6bd07ea279"
+  version "5.7.4"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.4.tgz#3e8d8a9947d0599a1796d10225d7432f4a4acf5e"
+  integrity sha512-1D++VG7BhrtvQpNbBzovKNc1FLGGEE/oGe7b9xJm/RFHMBeUaUGpluV9RLjZa47YFdPcDAenEYuq9pQPcMdLJg==
 
 acorn@^6.0.1:
   version "6.4.0"