Fix positional parameter warnings

[straight-shoota]

Fixes these warnings for positional parameter mismatches. This warning was introduced in Crystal 1.5.0 (crystal-lang/crystal#11915 crystal-lang/crystal#12167).

In spec/custom_drivers_types_spec.cr:55:34

 55 | def build_prepared_statement(command) : DB::Statement
                                   ^------
Warning: positional parameter 'command' corresponds to parameter 'query' of the overridden method DB::Connection#build_prepared_statement(
query), which has a different name and may affect named argument passing

In spec/custom_drivers_types_spec.cr:59:36

 59 | def build_unprepared_statement(command) : DB::Statement
                                     ^------
Warning: positional parameter 'command' corresponds to parameter 'query' of the overridden method DB::Connection#build_unprepared_statemen
t(query), which has a different name and may affect named argument passing