Nomenclature of Property and column name SNRRatio

Apologies for this very mundane and minor "issue"... I raise this as you might want to adapt it, otherwise please just ignore.

Both the property and the column name of the signal-to-noise ratio have two Rs in their name, while one R (i.e., SNRatio) seems more natural.

```
sourcextractor++ --property-column-mapping-all
[...]
SNRRatio:
  - snrratio : The object signal-to-noise ratio
```