Build with API version 2.12-SNAPSHOT and fix build errors

Change-Id: I4c0385bdc4242dd01fbca5ad2c812091b5ed6043

gradle.properties

diff --git a/gradle.properties b/gradle.properties
index 84e72a9..9d7322f 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -1,2 +1,2 @@
 apiType=plugin
-apiVersion=2.11-SNAPSHOT
+apiVersion=2.12-SNAPSHOT

src/main/java/com/googlesource/gerrit/plugins/rabbitmq/Properties.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/Properties.java b/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/Properties.java
index 418453c..998dfaa 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/Properties.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/Properties.java
@@ -56,7 +56,7 @@
   @Inject
   public Properties(final SitePaths site, @GerritServerConfig final Config config) {
     this.config = config;
-    this.pluginConfig = getPluginConfig(new File(site.etc_dir, CONFIG_FILENAME));
+    this.pluginConfig = getPluginConfig(new File(site.etc_dir.toFile(), CONFIG_FILENAME));
     this.properties = generateBasicProperties();
   }