Fixes CVE-2018-5147
- Change PKG_SOURCE_URL
fatal: unable to access 'https://git.xiph.org/tremor.git/': Failed to connect to git.xiph.org port 443: Connection refused
because they changed the URL of the repository
- Removes PKG_SOURCE_SUBDIR and PKG_SOURCE
Those are already defaults
- Fix indentation in description
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>