Update sbt-protobuf to 0.8.3 (#283)

Author: scala-steward

project/plugins.sbt

@@ -4,4 +4,4 @@ addSbtPlugin("org.scalameta"  % "sbt-scalafmt" % "2.5.5")
 addSbtPlugin("org.scalameta"  % "sbt-mdoc"     % "2.7.2")
 addSbtPlugin("com.github.sbt" % "sbt-release"  % "1.4.0")
 addSbtPlugin("com.github.sbt" % "sbt-git"      % "2.1.0")
-addSbtPlugin("com.github.sbt" % "sbt-protobuf" % "0.8.2")
+addSbtPlugin("com.github.sbt" % "sbt-protobuf" % "0.8.3")