Fix boot error in analytics config-checker code...

[JSegrave-IBM]

Fixing this error:

AssertionError: 
CONFIG ISSUE (1) : prometeo_config.json : One or more of the 'gas_limits' configurations [8, 6, 4, 2, 1] is incompatible with the range of the 'nitrogen_dioxide' sensor (min: 0.05, max: 10).
Please note that sensors must have a much larger range than the limits - 2x being a minimum.

Sensors can now report 'range exceeded', so the config-checker code no longer needs to enforce the above as a safety constraint. However they do still recommend it, via this non-fatal warning:

WARNING:GasExposureAnalytics:prometeo_config.json : One or more of the 'gas_limits' configurations [8, 6, 4, 2, 1] is very close to the range of the 'nitrogen_dioxide' sensor (min: 0.05, max: 10).
Sensors shoud have a much larger range than the limits - e.g. 2x at a minimum.

[JSegrave-IBM]

@lidderupk @narengan - here's the fix to that boot-up issue we saw tonight. Would you mind reviewing/merging this fix please? Thanks!

[JSegrave-IBM]

Linking issue #117

[upkarlidder]

Thanks John.