Update dependency unfetch to v3.1.2

Author: renovate-bot

package.json

@@ -38,7 +38,7 @@
     "@turf/helpers": "6.1.4",
     "es6-promise": "4.2.5",
     "mapbox-gl": "0.49.0",
-    "unfetch": "3.1.1"
+    "unfetch": "3.1.2"
   },
   "devDependencies": {
     "@babel/core": "^7.0.0-beta.54",