Bump marshmallow from 3.15.0 to 3.16.0 (#376)

dependabot[bot] · web-flow · commit b3a926a314b1 · 2022-05-30T18:52:44.000Z
diff --git a/requirements.txt b/requirements.txt
@@ -8,7 +8,7 @@ attrs==21.2.0
     # via -r requirements.in
 iso3166==2.0.2
     # via -r requirements.in
-marshmallow==3.15.0
+marshmallow==3.16.0
     # via
     #   -r requirements.in
     #   marshmallow-enum
