add warning is case 'rosdep update' is invoked as root (fix #258)
add warning is case 'rosdep update' is invoked as root (fix #258)

allenh1/rosdep,aymanim/rosdep,spaghetti-/rosdep,alessandro-aglietti/rosdep,ros-infrastructure/rosdep,georgepar/rosdep,georgepar/rosdep,allenh1/rosdep,wkentaro/rosdep,ros-infrastructure/rosdep,wkentaro/rosdep,alessandro-aglietti/rosdep,spaghetti-/rosdep,sorki/rosdep,sorki/rosdep,aymanim/rosdep