PSR7 Stream Fix

Minor fixes

-fix response handling as a Stream.

Update Guzzle version

Minor Changes

#3 Update Guzzle version to 6.

• Need to check the compatible of other libs;
• Compatible with PHP >5.5.

Check service response

Fixes

• Add empty response check and rise error.

Just small fixes

Merge pull request #1 from hugofcampos/release/0.3.0

Changelog

- Frete.co support

Frete.co support

0.3.0-apha

Add Frete.co support

Frete.co support

0.3.0

Add Frete.co support