Use MIT license in gem2deb copyright template

[Balasankar C <balasankarc@autistici.org>]

Hi all,

Currently, the template copyright file that is generated by gem2deb uses 
GPL-2.0+ as a placeholder license. Since a majority of the Ruby gems are 
under MIT/Expat license, can we use that instead? I had opened a bug[0] 
long back about it, but had forgotten about that. I understand using a 
better tool to identify the license and fill the copyright file using 
that info is the optimal solution. But this seems like a quick and 
harmless fix. If no one objects, I intend to make this change in the 
gem2deb repo by this weekend.

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=786521

Regards

Balasankar C