Update import order in kalibr_calibrate_cameras to fix cv_bridge_boos…

…t exception

ros-perception/vision_opencv#339
https://answers.ros.org/question/362388/cv_bridge_boost-raised-unreported-exception-when-importing-cv_bridge/

aslam_offline_calibration/kalibr/python/kalibr_calibrate_cameras

@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 print("importing libraries")
 import rosbag
+import cv2
 import cv_bridge
 
 import sm
@@ -11,7 +12,6 @@ import aslam_cv_backend as acvb
 import kalibr_common as kc
 import kalibr_camera_calibration as kcc
 
-import cv2
 import os
 import numpy as np
 import multiprocessing