Using `flatpak-builder-args` breaks Flatter

[PhrozenByte]

One can use neither the suggested --default-branch=nightly, nor --skip-if-unchanged options of flatpak-builder (see README.md) using the flatpak-builder-args option:

• --default-branch=nightly causes flatpak build-bundle to fail later, because it apparently still assumes master as branch name
• --skip-if-unchanged causes flatpak-builder to exit with code 42 (as documented by flatpak-builder), being interpreted as build failure by Flatter

[andyholmes]

I think I've got --skip-if-unchanged handled, although I don't have a test setup. Still not sure about --default-branch though, I think the master branch part is entrenched in flatpak-builder.

[andyholmes]

Sorry, --skip-if-unchanged was not actually fixed, but proper fix incoming momentarily.