Always run tests with utf-8 encoding

and do not rely on a utf-8 system locale.
Fixes LC_ALL=C mvn test

Change-Id: I3c64a95fada321c8b12d930137c8107f584b3a37
diff --git a/pom.xml b/pom.xml
index 72d13b4..0d6236b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -230,6 +230,13 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <configuration>
+          <argLine>-Dfile.encoding=UTF-8</argLine>
+        </configuration>
+      </plugin>
     </plugins>
   </build>
 </project>