Issue with Unirest config

[kpe09]

The Unirest configuration is applied every time an action is executed, meaning the configured default header is also being appended with every execution, because the Unirest client is a singleton. In projects with a high number of modules, this can lead to the header being too big and then causing a broken pipe. The fix is simple: the method addDefaultHeader(...) needs to be replaced with setDefaultHeader(...). I have already created a pull request with the necessary fix:
#420