chore(deps): update dependency lerna to v6

Author: renovate[bot]

package.json

@@ -11,7 +11,7 @@
     "node": ">= 8.9.0"
   },
   "devDependencies": {
-    "lerna": "3.13.1",
+    "lerna": "6.6.2",
     "prettier": "^1.14.2",
     "tslint": "^5.11.0",
     "typescript": "^3.0.3"