Exclusion constraint on ENUM errors: data type dow has no default operator class for access method "gist"
This is apparently a known issue, and it was fixed in PostgreSQL 10. The new version of btree_gist (10+) has in the docs,


  btree_gist provides GiST index operator classes that implement B-tree equivalent behavior for the data types int2, int4, int8, float4, float8, numeric, timestamp with time zone, timestamp without time zone, time with time zone, time without time zone, date, interval, oid, money, char, varchar, text, bytea, bit, varbit, macaddr, macaddr8, inet, cidr, uuid, and all enum types.