octave-specfun: license change from GPLv2+ to GPLv3+

[Thomas Sailer]

I'd like to push octave-specfun v1.1.0 to rawhide; octave-specfun
changes the license from GPLv2+ to GPLv3+.

The only package that depends on octave-specfun in the repository that I
am aware of is octave-signal, and that is already GPLv3+.

Are there any objections?

Thanks,
Tom