Theme of Qt5 app broken in 18.10

[pachulo]

You need to build it in an Ubuntu 18.04 environment. Snapcraft version 3.0 should fix these kind of issues, by using virtual machines to do the builds:

Call for testing: snapcraft 3.0

Hello Snapcrafters! The Snapcraft team is delighted to announce that version 3.0 is now available. Traditionally, the only base that has existed was derived from Ubuntu 16.04 LTS. With the release of Ubuntu 18.04 LTS a new base was created. The current architecture also allows for other bases to exist, such as one derived from Fedora. Building a snap with no base requires developers build on Ubuntu 16.04 LTS; the introduction of bases and build environments in snapcraft 3.0 automatically provis…