...

android {

    // GET THE DATA OF THE OPERATING SYSTEM WHERE ANDROID STUDIO IS RUN
    String osName = org.gradle.internal.os.OperatingSystem.current().getName();
    String osVersion = org.gradle.internal.os.OperatingSystem.current().getVersion();

    signingConfigs {
        config {

            // VALIDATE IF THE OPERATING SYSTEM IS WINDOWS OR MAC
            if (org.gradle.internal.os.OperatingSystem.current().isWindows()) {
                println "*** $osName $osVersion was detected."

                keyAlias ''
                keyPassword ''
                storeFile file('D:/..')
                storePassword 'chazkikey'

            } else if (org.gradle.internal.os.OperatingSystem.current().isMacOsX()) {
                println "*** S.O. es $osName $osVersion."

                keyAlias ''
                keyPassword ''
                storeFile file('/Users/Home/Documents/..')
                storePassword ''
            }
        }
    }

    ...
}

dependencies {
    ...
}

apply plugin: 'com.google.gms.google-services'