Fix checkstyle failing on autogenerated sources

This patch forces checkstyle to consider only the project
source directory

Change-Id: Ifb14b2a5a37fa6ba75b2b299f4eb379db7df65d8
diff --git a/lib/pom.xml b/lib/pom.xml
index 88c722f..45fbf18 100644
--- a/lib/pom.xml
+++ b/lib/pom.xml
@@ -919,6 +919,7 @@
                     <logViolationsToConsole>true</logViolationsToConsole>
                     <includeTestSourceDirectory>true</includeTestSourceDirectory>
                     <includeResources>false</includeResources>
+                    <sourceDirectories>${project.build.sourceDirectory}</sourceDirectories>
                 </configuration>
                 <executions>
                     <execution>