Add field name to ValueError raised by field adapter

[Gadgetoid]

The use of "f" string formatting is failing in both Python 2.7 and 3.5. You should swap this with "".format(), but otherwise this looks good! Thanks for raising a PR.

[coveralls]

Pull Request Test Coverage Report for Build 28

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.9%) to 97.642%

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Files with Coverage Reduction	New Missed Lines	%
i2cdevice/init.py	2	97.33%
<!--	Total:	2		-->

Totals
Change from base Build 25:	-0.9%
Covered Lines:	207
Relevant Lines:	212

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💛 - Coveralls

[Gadgetoid]

Thank you! I'll add a test for this error case to stop Coveralls from complaining.

[Gadgetoid]

I wonder if this is worth adding to KeyError and IndexError too since it would make uncaught exceptions in i2cdevice a little more useful to end-users. 🤔