Change model failures to slightly more likely mistake.

[luciansmith]

The original version of these files was indeed wrong as per the failure they are supposed to test, but it's slightly more likely that someone might make a mistake putting in a correctly-spelled-but-incorrectly-placed 'modifierSpeciesReference' than they are to put in an incorrectly-spelled-and-also-incorrectly-placed 'modiferSpeciesReference'.

See #372.