Automatic CI build fails because of multiple solution files

https://ci.appveyor.com/project/RoarFredriksen/amstomqttbridge/build/1.0.18:

```bash
Build started
git clone -q https://github.com/roarfred/AmsToMqttBridge.git C:\projects\amstomqttbridge
git fetch -q origin +refs/pull/37/merge:
git checkout -qf FETCH_HEAD
Specify which project or solution file to use because the folder contains more than one project or solution file.
```