fix base64 bug (#412)

* fix base64 bug

The Base64 table has Char '+' [https://en.wikipedia.org/wiki/Base64](https://en.wikipedia.org/wiki/Base64), it will turn to blank characters in url request, It will cause some error when  deserializeState the state.

* Fix encodeURIComponent for serialize

lib/routing.js

@@ -50,11 +50,13 @@ const reverseMappings = mappings.map(mapping =>
 )
 
 export const serializeState = state => {
-  const stateString = encodeURIComponent(JSON.stringify(state))
+  const stateString = JSON.stringify(state)
 
-  return typeof window !== 'undefined'
-    ? btoa(stateString)
-    : Buffer.from(stateString).toString('base64')
+  return encodeURIComponent(
+    typeof window !== 'undefined'
+      ? btoa(stateString)
+      : Buffer.from(stateString).toString('base64')
+  )
 }
 
 export const deserializeState = serializedState => {