code type is case sensitive, Java can not render java style

[xwjie]

in marddown file, when insert code, the code type is case sensitive, Java can not render with java style.

// in github , ```Java``` can render with java style, but vuepress can not, must be ```java```
int i = 0;

[xwjie]

XML also can not render correct

for example:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-security</artifactId>
</dependency>

[ulivz]

Fixed at 5e87b65

[ulivz]

Will release it at 0.9.0: #419. 🚀