Bump acorn from 5.5.3 to 5.7.4

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

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

package-lock.json

@@ -333,9 +333,9 @@
       "dev": true
     },
     "acorn": {
-      "version": "5.5.3",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-5.5.3.tgz",
-      "integrity": "sha512-jd5MkIUlbbmb07nXH0DT3y7rDVtkzDi4XZOUVWAer8ajmF/DTSSbl5oNFyDOl/OXA33Bl79+ypHhl2pN20VeOQ=="
+      "version": "5.7.4",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-5.7.4.tgz",
+      "integrity": "sha512-1D++VG7BhrtvQpNbBzovKNc1FLGGEE/oGe7b9xJm/RFHMBeUaUGpluV9RLjZa47YFdPcDAenEYuq9pQPcMdLJg=="
     },
     "acorn-globals": {
       "version": "4.1.0",