Added missing comma to spec_helper.rb when generated using the -t command

This fixes the first issue described here:
https://github.com/padrino/padrino-framework/issues/1296

where the spec_helper.rb generated by the command:
> padrino generate project test -b true -t rspec -e erb

creates a spec_helper.rb that is missing a comma at this line:
>def app(app = nil &blk)

The only change made is making the above line this:
> def app(app = nil, &blk)

in the files located at padrino-gen/lib/padrino-gen/generators/components/tests/