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/bme280.py

@@ -3,9 +3,8 @@
 # Copyright (C) 2020  Eric Callahan <arksine.code@gmail.com>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
-
-import bus
 import logging
+from . import bus
 
 REPORT_TIME = .8
 BME280_CHIP_ADDR = 0x76