Got out of memory when building the source code

[WillemJiang]

I tried to build the 2.6.2 source code by running "mvn clean install" from the route, I got the out of memory here. If I comment out the checkstyle check, I can run the test and build the kit.

Here is my box information:
Apache Maven 3.5.2 (138edd61fd100ec658bfa2d307c43b76940a5d7d; 2017-10-18T15:58:13+08:00)
Maven home: /opt/apache-maven-3.5.2
Java version: 1.8.0_151, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_151.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.12.6", arch: "x86_64", family: "mac"

[chickenlj]

I guess it's mainly caused by the rat and style plugin.

I have set them closed by default and only open on travis.
https://github.com/apache/incubator-dubbo/blob/413a2a0288d0b0800234132aff9f7c5f3803b633/pom.xml#L124