Bump acorn from 5.5.3 to 5.7.4 (#22)

Bumps [acorn](https://github.com/acornjs/acorn) from 5.5.3 to 5.7.4.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@5.5.3...5.7.4)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

yarn.lock

@@ -31,8 +31,8 @@ acorn-globals@^4.1.0:
     acorn "^5.0.0"
 
 acorn@^5.0.0, acorn@^5.3.0:
-  version "5.5.3"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.5.3.tgz#f473dd47e0277a08e28e9bec5aeeb04751f0b8c9"
+  version "5.7.4"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.4.tgz#3e8d8a9947d0599a1796d10225d7432f4a4acf5e"
 
 ajv@^4.9.1:
   version "4.11.8"