export plugin classes correctly

Author: itsankit-google

db2-plugin/pom.xml

@@ -98,7 +98,7 @@
         <configuration>
           <instructions>
             <_exportcontents>
-                io.cdap.plugin.db2.*
+                io.cdap.plugin.db2.*;
                 io.cdap.plugin.db.source.*;
                 io.cdap.plugin.db.sink.*;
                 org.apache.commons.lang;