If you are migrating to 1.0.0 you need to change the following properties.
In the Project's build.gradle file you need to replace minifyEnabled.
Hence your new build type should be
buildTypes {
release {
minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
}
}
Also make sure that gradle version is 1.0.0 like
classpath 'com.android.tools.build:gradle:1.0.0'
in the build.gradle file.
This should solve the problem.
Source: http://tools.android.com/tech-docs/new-build-system/migrating-to-1-0-0