Adapt to changed API in Gerrit core for creating metric fields

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I52c140f1321c0c3ebcfbbb2584a547bf5a1408a7

src/main/java/com/googlesource/gerrit/plugins/hooks/HookMetrics.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/hooks/HookMetrics.java b/src/main/java/com/googlesource/gerrit/plugins/hooks/HookMetrics.java
index 9b0bc82..c2046a1 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/hooks/HookMetrics.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/hooks/HookMetrics.java
@@ -31,7 +31,7 @@
 
   @Inject
   HookMetrics(MetricMaker metricMaker) {
-    Field<String> field = Field.ofString("hook");
+    Field<String> field = Field.ofString("hook").build();
     latency =
         metricMaker.newTimer(
             "latency",