update.sh: Use http instead of https

The reasons I propose the change are:

-   The certificate of https://archive.raspbian.org/ has expired on Oct 1.

    I assume this is temporary. See #133.

-   `https` MAY not be necessary here. (Only merge this commit if it _really_ is not necessary.)
Merge branch 'v1.1.x-http-archive' into packt

Conflicts:
	update.sh
.gitignore: Ignore autobuild artefacts