Suppress deprecation warning due to v1 backwards compatibility

[lukaskurz]

As mentioned in #39 , the deprecation warning for still using the Registrar can be suppressed, since it's still used for maintaining backwards compatibility.

[nohli]

@Purus could you merge and publish this, so the two build warnings disappear? 🙏🏽

/Users/achim/flutter/.pub-cache/hosted/pub.dartlang.org/launch_review-3.0.1/android/src/main/java/com/iyaffle/launchreview/LaunchReviewPlugin.java:11: warning: [deprecation] Registrar in PluginRegistry has been deprecated
import io.flutter.plugin.common.PluginRegistry.Registrar;
                                              ^
/Users/achim/flutter/.pub-cache/hosted/pub.dartlang.org/launch_review-3.0.1/android/src/main/java/com/iyaffle/launchreview/LaunchReviewPlugin.java:41: warning: [deprecation] Registrar in PluginRegistry has been deprecated
    public static void registerWith(Registrar registrar) {
                                    ^
2 warnings

[lukaskurz]

I'm not sure whether the maintainer of this repo is still active 🤷‍♂️