fix the print string formatting

[FoamyGuy]

Somehow I dropped a : from the string format causing a KeyError, this change adds the missing one to resolve the error.

[evaherrada]

Looks good to me. Although I haven't tested with hardware, the string formatting shouldn't be hardware dependent, and I did test it in a REPL just to be sure.

[caternuson]

unsophisticated test:

>>> print("heading: {.2f} degrees".format(42))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 
>>> print("heading: {:.2f} degrees".format(42))
heading: 42.00 degrees
>>>

[evaherrada]

Merging