scala sbt使用阿里云的maven repository

在中国，sbt访问maven-central很慢，可以改用阿里云的maven repository，或者jcenter作为备选

在.sbt目录下，新建或修改repositories文件

[repositories]
local
aliyun: http://maven.aliyun.com/nexus/content/groups/public
jcenter: http://jcenter.bintray.com
typesafe: http://repo.typesafe.com/typesafe/ivy-releases/, [organization]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext], bootOnly