fix docstring (#1818)
fix docstring (#1818)

change string to docstring
Endika/flask,fkazimierczak/flask,auready/flask,fkazimierczak/flask,tristanfisher/flask,auready/flask,Endika/flask,drewja/flask,pallets/flask,pallets/flask,karlw00t/flask,drewja/flask,antsar/flask,dawran6/flask,dawran6/flask,karlw00t/flask,hyunchel/flask,hyunchel/flask,wldtyp/flask,wldtyp/flask,antsar/flask,adrianmoisey/cptdevops,mitsuhiko/flask,tristanfisher/flask,adrianmoisey/cptdevops,fkazimierczak/flask,mitsuhiko/flask,pallets/flask,drewja/flask