Upgrade lerna to 3.15 (#26)

In doing so, fixes this vulnerability:
https://github.com/trialspark/enzyme-context/network/alert/yarn.lock/handlebars/open

### All Submissions:

* [x] Have you followed the guidelines in our Contributing document?
* [x] Have you checked to ensure there aren't other open [Pull Requests](../../pulls) for the same update/change?
* [x] Have you added an explanation of what your changes do and why you'd like us to include them?
* [x] Have you written new tests for your core changes, as applicable?
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package.json

@@ -22,10 +22,10 @@
     "graphql": "^14.0.2",
     "graphql-tag": "^2.10.0",
     "husky": "^1.1.4",
-    "jest": "^23.6.0",
+    "jest": "^24.8.0",
     "jest-environment-enzyme": "^7.0.1",
     "jest-enzyme": "^7.0.1",
-    "lerna": "^3.4.3",
+    "lerna": "^3.15.0",
     "lint-staged": "^8.0.5",
     "prettier": "^1.15.2",
     "prop-types": "^15.6.2",