Fixed #32 issues with error handling

[Kanosakl]

Was having a lot of confusion with this issue myself until I notice that the error reason resides in the body instead of in the response itself. I've added statusBody into the error object itself which allow me to get detailed message on what went wrong.

changes are on line 390 in ApiClient.js

   if (response.statusCode >= 400) {
                  _this.debug('error response', {
                    statusCode: response.statusCode,
                    statusMessage: response.statusMessage
                  });
                  reject({statusCode: response.statusCode, statusMessage: response.statusMessage, statusBody: body});
                }

(PS: my first pull request, sorry in advance if there's any mistake)

[cyrillef]

I took the changes, but the merge tool was not taking the code change properly. So I reject this PR but submitted the code changes in the master branch. Code change accepted.