Upgrade Inastacast to v1.2.6

Instacast version 1.2.6 is available for download from vemedio with sha256
560922bd0ccc7ebab002035d80ae4e630d6f30fde7eebacb7dff616e633a1a4d.
Upgraded the formula to install this version.
Merge pull request #6188 from asmod3us/instacast-126

Upgrade Instacast to v1.2.6