fix javadoc.io badge

Author: okue

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://travis-ci.org/line/line-bot-sdk-java.svg?branch=master)](https://travis-ci.org/line/line-bot-sdk-java)
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.linecorp.bot/line-bot-model/badge.svg)](https://maven-badges.herokuapp.com/maven-central/com.linecorp.bot/line-bot-model)
-[![javadoc.io](https://javadocio-badges.herokuapp.com/com.linecorp.bot/line-bot-model/badge.svg)](https://javadocio-badges.herokuapp.com/com.linecorp.bot/line-bot-model)
+[![javadoc](https://javadoc.io/badge2/com.linecorp.bot/line-bot-model/javadoc.svg)](https://javadoc.io/doc/com.linecorp.bot/line-bot-model)
 [![codecov](https://codecov.io/gh/line/line-bot-sdk-java/branch/master/graph/badge.svg)](https://codecov.io/gh/line/line-bot-sdk-java)
 
 
@@ -113,7 +113,7 @@ Community Q&A: https://www.line-community.me/questions
 
 News: https://developers.line.biz/en/news/
 
-Twitter: [@LINE_DEV](https://twitter.com/LINE_DEV) 
+Twitter: [@LINE_DEV](https://twitter.com/LINE_DEV)
 
 
 ## Versioning