This PR

• removes any checks from the build command of the release tool except the check for a clean working tree
• makes CMake 3.1 the minimum required version
• updates the Docker file to use a not-so-ancient CMake version and Qt 5.9

Types of changes

• ✅ Bug fix (non-breaking change which fixes an issue)

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED]
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]