Fix maven encoding warning

Change-Id: I550e8640abd3fddd8d41a095805f7d4019c977db

pom.xml

diff --git a/pom.xml b/pom.xml
index fa45050..3b9cd58 100644
--- a/pom.xml
+++ b/pom.xml
@@ -27,6 +27,7 @@
   <properties>
     <Gerrit-ApiType>plugin</Gerrit-ApiType>
     <Gerrit-ApiVersion>2.9.1</Gerrit-ApiVersion>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>
 
   <build>