Adding sources for plugin via Gradle

I've setup an IntelliJ plugin using Gradle. My build.gradle file contains

plugins {
    id 'java'
    id 'org.jetbrains.intellij' version '0.3.12'
}

//...

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

intellij {
    version '2018.2.4'
    plugins 'git4idea'
}

Is there any way how I can include the sources of the Git4Idea plugin to the project?