Specify UTF-8

- to suppress "[WARNING] Using platform encoding ..." warnings.

Change-Id: I817e3c404cb7c19b4854f442a59267deb67212a6

@@ -53,6 +53,10 @@
         </developer>
     </developers>
 
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
     <distributionManagement>
         <snapshotRepository>
             <id>ossrh</id>