fix: build_parameter_query can't decode utf-8 charcters in parameters.py

Hi,
I found utf-8 probrem when I execute `aws elasticbeanstalk create-application-version` 
with argument  `--description=[UTF-8 CHARACTERS]`.

It seems this bug  is related to https://github.com/aws/aws-cli/issues/593,  so
I modify `build_parameter_query` in order to decode utf-8 characters.

Thanks.