Bump rollup from 1.32.1 to 2.6.1

Bumps [rollup](https://github.com/rollup/rollup) from 1.32.1 to 2.6.1.
- [Release notes](https://github.com/rollup/rollup/releases)
- [Changelog](https://github.com/rollup/rollup/blob/master/CHANGELOG.md)
- [Commits](rollup/rollup@v1.32.1...v2.6.1)

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

package.json

@@ -58,7 +58,7 @@
     "karma-mocha": "^1.3.0",
     "mocha": "^7.1.1",
     "prettier": "2.0.4",
-    "rollup": "^1.18.0",
+    "rollup": "^2.6.1",
     "rollup-plugin-node-resolve": "^5.2.0",
     "rollup-plugin-serve": "^1.0.1",
     "rollup-plugin-terser": "^5.3.0",