[skip ci] Fixing issue creating javadoc with new Java versions

Author: Chris Wiechmann

pom.xml

@@ -312,6 +312,9 @@
 						<groupId>org.apache.maven.plugins</groupId>
 						<artifactId>maven-javadoc-plugin</artifactId>
 						<version>2.9.1</version>
+						<configuration>
+							<source>8</source>
+						</configuration>
 						<executions>
 							<execution>
 								<id>attach-javadocs</id>