build(deps): bump acorn from 5.7.1 to 5.7.4 in /ihaskell_labextension

Bumps [acorn](https://github.com/acornjs/acorn) from 5.7.1 to 5.7.4.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](https://github.com/acornjs/acorn/compare/5.7.1...5.7.4)
Signed-off-by: dependabot[bot] <support@github.com>

ihaskell_labextension/package-lock.json

@@ -560,9 +560,9 @@
       }
     },
     "acorn": {
-      "version": "5.7.1",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-5.7.1.tgz",
-      "integrity": "sha512-d+nbxBUGKg7Arpsvbnlq61mc12ek3EY8EQldM3GPAhWJ1UVxC6TDGbIvUMNU6obBX3i1+ptCIzV4vq0gFPEGVQ==",
+      "version": "5.7.4",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-5.7.4.tgz",
+      "integrity": "sha512-1D++VG7BhrtvQpNbBzovKNc1FLGGEE/oGe7b9xJm/RFHMBeUaUGpluV9RLjZa47YFdPcDAenEYuq9pQPcMdLJg==",
       "dev": true
     },
     "acorn-dynamic-import": {

ihaskell_labextension/yarn.lock

@@ -570,8 +570,8 @@ acorn-dynamic-import@^3.0.0:
     acorn "^5.0.0"
 
 acorn@^5.0.0, acorn@^5.6.2:
-  version "5.7.3"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.3.tgz#67aa231bf8812974b85235a96771eb6bd07ea279"
+  version "5.7.4"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.4.tgz#3e8d8a9947d0599a1796d10225d7432f4a4acf5e"
 
 ajv-keywords@^3.1.0:
   version "3.4.1"