fix(package): update deepmerge to version 3.0.0 (#129)

Author: greenkeeper[bot]

package.json

@@ -38,6 +38,6 @@
   },
   "dependencies": {
     "ajv": "^6.5.4",
-    "deepmerge": "^2.1.1"
+    "deepmerge": "^3.0.0"
   }
 }