fix: update dependency @reach/router to ^1.2.1 (#16797)

Author: renovate[bot]

packages/gatsby/package.json

@@ -20,7 +20,7 @@
     "@hapi/joi": "^15.1.1",
     "@mikaelkristiansson/domready": "^1.0.9",
     "@pieh/friendly-errors-webpack-plugin": "1.7.0-chalk-2",
-    "@reach/router": "^1.1.1",
+    "@reach/router": "^1.2.1",
     "address": "1.0.3",
     "autoprefixer": "^9.6.0",
     "axios": "^0.19.0",