extras: Use "from . import module" for relative imports

Use alternate import syntax to improve Python3 compatibility.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/bed_tilt.py

@@ -4,7 +4,8 @@
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 import logging
-import probe, mathutil
+import mathutil
+from . import probe
 
 class BedTilt:
     def __init__(self, config):