SchemeFromURL: return driver instead of database name

[MinhKhangCorp]

https://github.com/golang-migrate/migrate/blob/acc11eda6d266a4cc799bc5d7368b63c8a07beeb/migrate.go#L96

it's return "mysql" instead of "dbname" when we passs the url like : ""mysql://dev:dev@tcp(localhost:3306)/dbname?multiStatements=true"