Buck: Don't package gson library in shaded plugin jar

Change-Id: I1a8881de390b1eef933d62f0f05431aa5c704a77
diff --git a/BUCK b/BUCK
index 36a0c92..4d13766 100644
--- a/BUCK
+++ b/BUCK
@@ -7,7 +7,7 @@
     'Gerrit-Module: com.googlesource.gerrit.plugins.branchnetwork.GitCommitCacheModule',
     'Gerrit-HttpModule: com.googlesource.gerrit.plugins.branchnetwork.NetworkGraphModule'
   ],
-  deps = [
+  provided_deps = [
     '//lib:gson',
   ],
 )