fix(package): update deepmerge to version 4.1.1

Closes #138

Author: greenkeeper[bot]

package.json

@@ -7,7 +7,7 @@
     "@material-ui/core": "^3.9.3",
     "@material-ui/icons": "^3.0.2",
     "date-fns": "^2.0.0-alpha.27",
-    "deepmerge": "^3.2.0",
+    "deepmerge": "^4.1.1",
     "firebase": "^5.11.0",
     "i18next": "^15.1.0",
     "prop-types": "^15.7.2",