bump version to 0.3.21
bump version to 0.3.21

ros/catkin,thaddeustaylor/catkin,ros/catkin,jack-oquin/catkin,thaddeustaylor/catkin,harmishhk/catkin,scpeters/catkin,meyerj/catkin,asmodehn/catkin,shyamalschandra/catkin,wkentaro/catkin,asmodehn/catkin,scpeters/catkin,wkentaro/catkin,beni55/catkin,jack-oquin/catkin,meyerj/catkin,asmodehn/catkin,harmishhk/catkin,scpeters/catkin,jack-oquin/catkin,wkentaro/catkin,ros/catkin,thaddeustaylor/catkin,beni55/catkin,beni55/catkin,shyamalschandra/catkin,meyerj/catkin,shyamalschandra/catkin,harmishhk/catkin