Upgrade maven-compiler-plugin.
diff --git a/pom.xml b/pom.xml
index 75a4a3d..d88608a 100644
--- a/pom.xml
+++ b/pom.xml
@@ -339,7 +339,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
-                <version>2.0</version>
+                <version>3.6.1</version>
                 <configuration>
                     <source>1.6</source>
                     <target>1.6</target>