Add dependency: smbus2

[NicolaiSoeborg]

Fixes:

>>> import bme680                                                                                                                                                                                          
>>> sensor = bme680.BME680(bme680.I2C_ADDR_PRIMARY)                                                                                                                                                        
Traceback (most recent call last):                                                                                                                                                                         
  File "<stdin>", line 1, in <module>                                                                                                                                                                      
  File "/usr/local/lib/python3.7/dist-packages/bme680/__init__.py", line 22, in __init__                                                                                                                   
    import smbus                                                                                                                                                                                           
ModuleNotFoundError: No module named 'smbus'                                                                                                                                                               

[coveralls]

Pull Request Test Coverage Report for Build 34

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.275%

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Totals
Change from base Build 31:	0.0%
Covered Lines:	396
Relevant Lines:	459

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💛 - Coveralls

[Gadgetoid]

Thank you!

I tend to rely on "smbus" from apt since - despite maintaining the PyPI package I'm not sure how up-to-date it is with the officially distributed apt package. This is a pain because a PyPI package cannot specify an apt package as a dependency (without some horrible gymnastics that have no place in setup.py).

smbus2 doesn't provide the smbus package, but it might be appropriate to depend on smbus here since it seems to work fine and, god knows, I'm never going to be on the ball with fixing/updating it if nobody is using it.

So, TLDR: this should be "smbus" not "smbus2".

[Gadgetoid]

Thank you! Now we pray my smbus package isn't subtly broken in some way!