Upgrade to protobuf-gradle-plugin 0.8.18

Test: ./gradlew assembleDebug
Change-Id: Ice05dde588601893e9bbd572659aad8ca1736705
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 1246430..576df3e 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -141,7 +141,7 @@
 playServicesWearable = { module = "com.google.android.gms:play-services-wearable", version = "17.1.0" }
 protobuf = { module = "com.google.protobuf:protobuf-java", version = "3.4.0" }
 protobufCompiler = { module = "com.google.protobuf:protoc", version = "3.10.0" }
-protobufGradlePluginz = { module = "com.google.protobuf:protobuf-gradle-plugin", version = "0.8.16" }
+protobufGradlePluginz = { module = "com.google.protobuf:protobuf-gradle-plugin", version = "0.8.18" }
 protobufLite = { module = "com.google.protobuf:protobuf-javalite", version = "3.10.0" }
 reactiveStreams = { module = "org.reactivestreams:reactive-streams", version = "1.0.0" }
 retrofit = { module = "com.squareup.retrofit2:retrofit", version = "2.7.2" }