Bump acorn from 5.7.1 to 5.7.4

Bumps [acorn](https://github.com/acornjs/acorn) from 5.7.1 to 5.7.4.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@5.7.1...5.7.4)

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

Author: dependabot[bot]

yarn.lock

@@ -415,8 +415,8 @@ acorn-globals@^4.1.0:
     acorn "^5.0.0"
 
 acorn@^5.0.0, acorn@^5.3.0:
-  version "5.7.1"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.1.tgz#f095829297706a7c9776958c0afc8930a9b9d9d8"
+  version "5.7.4"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.4.tgz#3e8d8a9947d0599a1796d10225d7432f4a4acf5e"
 
 agent-base@5:
   version "5.1.1"