Android : signingConfigs tag giving me a Lint error in build.gradle after upgrading to v22

I've had the following code in my build.gradle (app) file for a while:

signingConfigs {
    release {
        storeFile file("D:\\Android\\keystore\\myApp.jks")
        storePassword "myStorePw"
        keyAlias "myKeyAlias"
        keyPassword "MyKeyPw"
    }
}

I've just upgraded to targetSdkVersion=22, which meant upgrading SDKs and build tools to 22 as well. Now that whole section is highlighted in yellow in Android Studio (141.1793788) with the message:

'signingConfigs' cannot be applied to '(groovy.land.Closure<com.android.build.gradle.internal.dsl.SigningConfig>)'

Has there been a change in v22 that I need to know about? I can't find documentation.