add sbt-protobuf in artifact-migrations.conf

- sbt/sbt-protobuf#74
- https://repo1.maven.org/maven2/com/github/sbt/sbt-protobuf_2.12_1.0/

Author: xuwei-k

modules/core/src/main/resources/artifact-migrations.conf

@@ -1,4 +1,10 @@
 changes = [
+  {
+    groupIdBefore = com.github.gseitz
+    groupIdAfter = com.github.sbt
+    artifactIdAfter = sbt-protobuf
+    initialVersion = 0.7.0
+  },
   {
     groupIdBefore = com.github.gseitz
     groupIdAfter = com.github.sbt