Using Android Gradle plugin 0.7.0 with the following build.gradle:
buildscript {
    repositories {
        mavenCentral()
    }
    dependenci         
        
Important to know in what file it comes to this error (in you example it is META-INF/LICENSE.txt) , in my case it was in META-INF/LICENSE [without ".txt"], and then in the file META-INF/ASL2.0 so I added to my build.gradle this lines:
android {
    packagingOptions {
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/ASL2.0'
    }
}
Very important (!) -> add the name of the file in the same style, that you see it in the error message: the text is case sensitive, and there is a difference between *.txt and *(without "txt").