Bump @rollup/plugin-commonjs from 14.0.0 to 15.0.0 (#264)

Bumps [@rollup/plugin-commonjs](https://github.com/rollup/plugins) from 14.0.0 to 15.0.0.
- [Release notes](https://github.com/rollup/plugins/releases)
- [Commits](rollup/plugins@commonjs-v14.0.0...commonjs-v15.0.0)

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

package.json

@@ -49,7 +49,7 @@
     "@babel/preset-env": "^7.6.3",
     "@babel/preset-typescript": "^7.6.0",
     "@open-wc/karma-esm": "^3.0.3",
-    "@rollup/plugin-commonjs": "^14.0.0",
+    "@rollup/plugin-commonjs": "^15.0.0",
     "@rollup/plugin-node-resolve": "^8.0.0",
     "@types/chai": "^4.2.4",
     "@types/mocha": "^8.0.0",