docs: Correct default value for routerMode (#549)

This was `history` when it should have been set to `hash`. It also described the correct value in the example, which was misleading.

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Author: niksudan

docs/configuration.md

@@ -368,7 +368,7 @@ window.$docsify = {
 ## routerMode
 
 - type: `String`
-- default: `history`
+- default: `hash`
 
 ```js
 window.$docsify = {