USB commands require --format json when it should default

[emarsman]

In some cases, USB commands require --format json, but that should be the default. Something in the auto-detect logic isn't working correctly.

File "/Users/Belina/openxc-python/openxc/sources/base.py", line 63, in streamer

raise MissingPayloadFormatError("Unable to auto-detect payload "

openxc.sources.base.MissingPayloadFormatError: Unable to auto-detect payload format, must specify manually with --format [json|protobuf]

[PPRAKA30]

Reference: #138