mysql@5.6: Update license to GPL-2.0-only
mysql@5.6: Update license to GPL-2.0-only

https://downloads.mysql.com/docs/licenses/mysqld-5.6-gpl-en.pdf page 2
says:

> Election of GPLv2
> For the avoidance of doubt, except that if any license choice other than
> GPL or LGPL is available it will apply instead, Oracle elects to use
> only the General Public License version 2 (GPLv2) at this time for any
> software where a choice of GPL license versions is made available with
> the language indicating that GPLv2 or any later version may be used, or
> where a choice of which version of the GPL is applied is otherwise
> unspecified.

dsXLII/homebrew-core,cblecker/homebrew-core,Moisan/homebrew-core,sjackman/homebrew-core,JCount/homebrew-core,zyedidia/homebrew-core,mfikes/homebrew-core,nandub/homebrew-core,filcab/homebrew-core,chrisfinazzo/homebrew-core,filcab/homebrew-core,Linuxbrew/homebrew-core,Moisan/homebrew-core,Homebrew/homebrew-core,mbcoguno/homebrew-core,spaam/homebrew-core,Homebrew/homebrew-core,mfikes/homebrew-core,lemzwerg/homebrew-core,adam-moss/homebrew-core,makigumo/homebrew-core,lemzwerg/homebrew-core,cblecker/homebrew-core,adam-moss/homebrew-core,uyjulian/homebrew-core,Linuxbrew/homebrew-core,stgraber/homebrew-core,nbari/homebrew-core,mbcoguno/homebrew-core,nandub/homebrew-core,sjackman/homebrew-core,nbari/homebrew-core,dsXLII/homebrew-core,chrisfinazzo/homebrew-core,spaam/homebrew-core,stgraber/homebrew-core,zyedidia/homebrew-core,JCount/homebrew-core,makigumo/homebrew-core,uyjulian/homebrew-core,mbcoguno/homebrew-core