OLD:
minecraft {
    version = "1.8.9-11.15.0.1690"
    runDir = "run"

    // the mappings can be changed at any time, and must be in the following format.
    // snapshot_YYYYMMDD   snapshot are built nightly.
    // stable_#            stables are built at the discretion of the MCP team.
    // Use non-default mappings at your own risk. they may not allways work.
    // simply re-run your setup task after changing the mappings to update your workspace.
    mappings = "stable_20"
    // makeObfSourceJar = false // an Srg named sources jar is made by default. uncomment this to disable.
}



NEW:
minecraft {
    version = "1.8.9-11.15.0.1690"
    runDir = "run"

    // the mappings can be changed at any time, and must be in the following format.
    // snapshot_YYYYMMDD   snapshot are built nightly.
    // stable_#            stables are built at the discretion of the MCP team.
    // Use non-default mappings at your own risk. they may not allways work.
    // simply re-run your setup task after changing the mappings to update your workspace.
    mappings = "snapshot_20160109"
    // makeObfSourceJar = false // an Srg named sources jar is made by default. uncomment this to disable.
}