Bump Gerrit to v3.9.0-rc2

Change-Id: I3fbb5fec28223410e5465e99b32f70ec74ca3a7f

build.sbt

diff --git a/build.sbt b/build.sbt
index 46b0942..4140349 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,6 +1,6 @@
 enablePlugins(GitVersioning)
 
-val gerritApiVersion = "3.8.0-rc4"
+val gerritApiVersion = "3.9.0-rc2"
 
 val pluginName = "analytics"