Bump GIF requirement to version 5.1 (#425)
Bump GIF requirement to version 5.1 (#425)

We use `DGifCloseFile` which in version 5.1 got an extra parameter
`int *ErrorCode` not present in 5.0. This means that we need at least
version 5.1 to compile.

Fixes #420
libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl