Change in coordinateUncertaintyInMeters term example based on the recommendation of best practices and quick guide

[RicardoOrtizG]

In chapter "1.6.15. GPS Accuracy", I think this is a very important recommendation for documentation that goes beyond the workflow of georeferencing and is necessary to document explicitly in the examples of the DwC term coordinateUncertaintyInMeters. Actually, the recommendation for unknown uncertainty doesn't match completely with the actual example of the term: "(reasonable lower limit of a GPS reading under good conditions if the actual precision was not recorded at the time). 71 (uncertainty for a UTM coordinate having 100-meter precision and a known spatial reference system)."

[tucotuco]

Term change requested in Darwin Core. Closing.