added check on constants.__dict__ for micropython support

[giampiero7]

In micropython the attribute dict is not available. I added a check to skip the export in this case.

[coveralls]

Pull Request Test Coverage Report for Build 19

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 53 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.05%) to 77.56%

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Files with Coverage Reduction	New Missed Lines	%
bme680/init.py	53	50.72%
<!--	Total:	53		-->

Totals
Change from base Build 18:	0.05%
Covered Lines:	356
Relevant Lines:	459

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💛 - Coveralls

[Gadgetoid]

Thank you- I'm surprised there's a MicroPython board this will run on, but then I'm only accustomed to the limits of the micro:bit.

[giampiero7]

I'm using it on Pycom, it runs with no issues. Best, Giampiero