Fabric build in Android Studio will generate folder "true" under project root folder?

Question

I am using Fabric in my project which works well. But I found a problem, when I start the fabric build, sometimes it will generate a new folder named "true" under project root folder, which contains only one file: crashlytics-build.properties. Is this folder necessary? Can I change crashlytics-build.properties generation location? Thanks.

My project has many modules, this is the gradle file for the root project:

buildscript {
    repositories {
        jcenter()
        maven { url 'https://maven.fabric.io/public' }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.3.1'
        classpath 'io.fabric.tools:gradle:1.+'
    }
}

allprojects {
    repositories {
        jcenter()
        maven { url 'https://maven.fabric.io/public' }
        flatDir{
            dirs '../libs'
        }
    }
}