Fix GetObservation invalid SRS exception code

Change exception code for invalid SRS prefixes (was NoApplicableCode, changed to InvalidParameterException). CITE test [getObservation:core-SOS.GetObservation-RequestInvalidSRSName.1](https://github.com/opengeospatial/ets-sos10/blob/master/src/main/scripts/ctl/GetObservation.xml#L23) was failing.