fix: upgrade rollup from 2.18.1 to 2.18.2

Snyk has created this PR to upgrade rollup from 2.18.1 to 2.18.2.

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

See this project in Snyk:
https://app.snyk.io/org/dmaccormack/project/51e346e8-0429-4dc8-902a-93e77d72b41c?utm_source=github&utm_medium=upgrade-pr

Author: snyk-bot

package-lock.json

@@ -42,7 +42,7 @@
     "jest": "^26.1.0",
     "jsdoc": "^3.6.4",
     "prettier": "^2.0.5",
-    "rollup": "^2.18.1",
+    "rollup": "^2.18.2",
     "rollup-plugin-babel": "^4.4.0",
     "rollup-plugin-eslint": "^7",
     "rollup-plugin-terser": "^6.1.0"