convert to new react native config format

package.json

     "filestream",
     "image header"
   ],
-  "rnpm": {
-    "commands": {
-      "prelink": "node ./node_modules/rn-fetch-blob/scripts/prelink.js"
-    }
-  },
   "repository": {
     "url": "https://github.com/joltup/rn-fetch-blob.git"
   },

react-native.config.js

+module.exports = {
+  dependency: {
+    hooks: {
+      prelink: 'node ./node_modules/rn-fetch-blob/scripts/prelink.js',
+    },
+  },
+};