Update dependency lerna to v6

Author: renovate[bot]

package.json

@@ -12,7 +12,7 @@
     "coveralls": "^3.0.9",
     "eslint": "^7.0.0",
     "eslint-plugin-import": "^2.22.0",
-    "lerna": "^4.0.0",
+    "lerna": "^6.0.0",
     "manual-git-changelog": "^1.0.1",
     "mocha": "^8.0.0",
     "nyc": "^15.0.0",