chore(deps): update dependency lerna to v6

Author: renovate[bot]

package.json

@@ -17,7 +17,7 @@
     "cross-env": "^5.2.0",
     "eslint": "^6.1.0",
     "husky": "^3.0.4",
-    "lerna": "^3.15.0",
+    "lerna": "^6.0.0",
     "lint-staged": "^9.2.4",
     "prettier": "^1.17.1",
     "typescript": "^3.5.3"