Bump karma from 3.1.3 to 6.3.16

Bumps [karma](https://github.com/karma-runner/karma) from 3.1.3 to 6.3.16.
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](karma-runner/karma@v3.1.3...v6.3.16)

---
updated-dependencies:
- dependency-name: karma
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

actioncable/package.json

@@ -28,7 +28,7 @@
     "@rollup/plugin-commonjs": "^19.0.1",
     "eslint": "^4.3.0",
     "eslint-plugin-import": "^2.7.0",
-    "karma": "^3.1.1",
+    "karma": "^6.3.16",
     "karma-chrome-launcher": "^2.2.0",
     "karma-qunit": "^2.1.0",
     "karma-sauce-launcher": "^1.2.0",