Update lerna from ^2.3.1 to 3.20.2

Author: dependencies-bot

package.json

@@ -25,7 +25,7 @@
     "codecov": "3.6.1",
     "husky": "3.0.9",
     "jest": "24.9.0",
-    "lerna": "^2.3.1",
+    "lerna": "3.20.2",
     "lint-staged": "9.4.2",
     "prettier-eslint-cli": "5.0.0"
   }