improve code style
fixed: after update api returns 0 days trial period (uncomment test)
improve comment
delete the workaround for empty array of offers instead NULL
add test for clientService
update dependencies
#44 response_code is now Integer instead of String
#23 now preauthorizations can be created with description
revert #44 response_code is now Integer instead of String
update project version and README
[maven-release-plugin] prepare release v3.2.0