Umlauts in milestone title: Unhandled promise rejection

[almereyda]

When trying to gtt report with

url: https://lab.allmende.io/api/v4/
token: 
project: degrowth/scriptorium
milestone: "Malmö 2018 II"

set, the command runs into a warning and continues to work indefinitely, without producing any network I/O.

$ gtt report
🔍  Selected projects: degrowth/scriptorium
🔍  Resolving "degrowth/scriptorium"... ✓
📦  Fetching issues... \(node:29091) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): StatusCodeError: 500 - {"message":"500 Internal Server Error"}
(node:29091) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:29091) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): StatusCodeError: 500 - {"message":"500 Internal Server Error"}
📦  Fetching issues... 

This is due to the Umlaut in the milestone title, and does not happen with soley ASCII characters present.