fix(package): update preact-router to version 3.1.0

Closes #341

Author: greenkeeper[bot]

package.json

@@ -91,7 +91,7 @@
     "preact": "^8.1.0",
     "preact-compat": "^3.15.0",
     "preact-render-to-string": "^3.6.0",
-    "preact-router": "^2.5.1",
+    "preact-router": "^3.1.0",
     "promise-polyfill": "^7.0.1",
     "proptypes": "^1.0.0",
     "sirv-cli": "^0.4.2"