Fix the incorrect dates listed in API documentation
Fix the incorrect dates listed in API documentation

We can just say "last five years" rather than giving precise dates.

Closes #1165

annapowellsmith/openpresc,ebmdatalab/openprescribing,ebmdatalab/openprescribing,ebmdatalab/openprescribing,annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc,ebmdatalab/openprescribing