Bump postcode from 0.2.5 to 5.1.0

Bumps [postcode](https://github.com/ideal-postcodes/postcode) from 0.2.5 to 5.1.0.
- [Release notes](https://github.com/ideal-postcodes/postcode/releases)
- [Changelog](https://github.com/ideal-postcodes/postcode/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ideal-postcodes/postcode/commits/5.1.0)

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -17,7 +17,7 @@
   },
   "dependencies": {
     "json-client": "^0.9.2",
-    "postcode": "^0.2.5"
+    "postcode": "^5.1.0"
   },
   "devDependencies": {
     "coveralls": "^3.1.0",