fix a spelling error in contributing.md
fix a spelling error in contributing.md

juliandunn/supermarket,rafaelmagu/supermarket,nellshamrell/supermarket,robbkidd/supermarket,chef/supermarket,leftathome/supermarket,jzohrab/supermarket,chef/supermarket,rafaelmagu/supermarket,juliandunn/supermarket,rafaelmagu/supermarket,robbkidd/supermarket,tas50/supermarket,juliandunn/supermarket,chef/supermarket,dpnl87/supermarket,dpnl87/supermarket,robbkidd/supermarket,nellshamrell/supermarket,rafaelmagu/supermarket,dpnl87/supermarket,juliandunn/supermarket,tas50/supermarket,leftathome/supermarket,robbkidd/supermarket,jzohrab/supermarket,tas50/supermarket,jzohrab/supermarket,leftathome/supermarket,chef/supermarket,dpnl87/supermarket,chef/supermarket,leftathome/supermarket,tas50/supermarket,jzohrab/supermarket,nellshamrell/supermarket,nellshamrell/supermarket