fix: upgrade opossum from 5.1.0 to 5.1.1 (#29)

Snyk has created this PR to upgrade opossum from 5.1.0 to 5.1.1.

See this package in npm:
https://www.npmjs.com/package/opossum

See this project in Snyk:
https://app.snyk.io/org/nodeshift-agg/project/1a94b58c-14a1-428b-be9b-51d8d1442586?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -26,7 +26,7 @@
     "codacy-coverage": "^3.4.0",
     "coveralls": "^3.1.0",
     "nyc": "^15.1.0",
-    "opossum": "^5.1.0",
+    "opossum": "^5.1.1",
     "standard-version": "^9.0.0",
     "standardx": "^5.0.0",
     "tap-spec": "^5.0.0",