Payment for MaestroCard on my Production app failing. 

Payment for Maestro Card on my Production apps is failing. Each time i keep getting ERROR:
 **"That payment method is unsupported. Please choose another one."**

When I check `ActiveMerchant::Billing::AuthorizeNetGateway.supports?('maestro')`
It Returns always `false` for `Maestro Cards`

So I forked it and add maestro as *SupportedCard* Types in *AuthorizeNetGateway*.
Also updated the corresponding test case which pass maestro credit card as well.

You can use the following test Maestro credit card  when testing your Authorize.net checkout:
**Maestro: 6759649826438453**

Test Result are as follows-:
```
bundle exec rake test:remote TEST=test/remote/gateways/remote_nab_transact_test.rb
/Users/vivek/.rvm/rubies/ruby-1.9.3-p327/bin/ruby -I"lib:test" -rubygems -w -I"/Users/vivek/.rvm/gems/ruby-1.9.3-p327/gems/rake-10.3.2/lib" "/Users/vivek/.rvm/gems/ruby-1.9.3-p327/gems/rake-10.3.2/lib/rake/rake_test_loader.rb" "test/remote/gateways/remote_nab_transact_test.rb"
Run options:

# Running tests:

....................

Finished tests in 134.124531s, 0.1491 tests/s, 0.7978 assertions/s.

20 tests, 107 assertions, 0 failures, 0 errors, 0 skips
````

Thanks