Fix IterableOnce foreach deprecation warning

Fixes following warning:
method foreach in class IterableOnceExtensionMethods is deprecated (since 2.13.0): Use .iterator.foreach(...) instead

Change-Id: I9fad75d232c1620d380cc40c303308abaf5319bf

src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala

diff --git a/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala b/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala
index 589a70d..585447f 100644
--- a/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala
+++ b/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala
@@ -31,7 +31,7 @@
   def format[T](values: IterableOnce[T], out: PrintWriter) = {
     val gson: Gson = gsonBuilder.create
 
-    for (value <- values) {
+    values.iterator.foreach {value =>
       gson.toJson(value, out)
       out.println()
     }