Switch to using Path instead of File for sitePaths

Gerrit core changed SitePaths to yield Paths instead of Files. Hence,
we follow that move.

Change-Id: Ibdac674adb7ebdf58f9e3d4752db8e8be7a5fd04

src/main/java/com/googlesource/gerrit/plugins/motd/MotdFileBasedConfig.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/motd/MotdFileBasedConfig.java b/src/main/java/com/googlesource/gerrit/plugins/motd/MotdFileBasedConfig.java
index 07e5772..7d79d8b 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/motd/MotdFileBasedConfig.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/motd/MotdFileBasedConfig.java
@@ -43,7 +43,7 @@
   @Inject
   public MotdFileBasedConfig(final SitePaths site)
       throws ConfigInvalidException, IOException {
-    this.cfgPath = new File(site.etc_dir, "motd.config");
+    this.cfgPath = new File(site.etc_dir.toFile(), "motd.config");
     log.info("Loading configuration from " + cfgPath);
     this.config = new FileBasedConfig(cfgPath, FS.DETECTED);
     this.subnets = allSubnets();