Add another covid grounding map entry
Add another covid grounding map entry

pH is typically correctly grounded to MESH:D006863 but there are over
300 stmts in the cord19 model where REACH had grounded it to the gene PPY

johnbachman/indra,sorgerlab/belpy,johnbachman/indra,johnbachman/belpy,sorgerlab/indra,bgyori/indra,sorgerlab/belpy,johnbachman/belpy,bgyori/indra,sorgerlab/indra,sorgerlab/belpy,johnbachman/indra,johnbachman/belpy,sorgerlab/indra,bgyori/indra