gpl.txt uses outdated gpl text

[knight-of-ni]

Sorry guys. I know this is another nitpick.

The verbiage in gpl.txt is outdated.

Oddly enough, this PR has the most recent version, but it seems it was not used:
https://github.com/msteinert/bstring/pull/120/changes

The difference is in the address. 51 Franklin street is the old address.

This sets off rpmlint alarms bells in Fedora. I imagine it would in Debian as well.

bstring.aarch64: E: incorrect-fsf-address /usr/share/licenses/bstring/gpl.txt
bstring.ppc64le: E: incorrect-fsf-address /usr/share/licenses/bstring/gpl.txt
bstring.s390x: E: incorrect-fsf-address /usr/share/licenses/bstring/gpl.txt
bstring.x86_64: E: incorrect-fsf-address /usr/share/licenses/bstring/gpl.txt
bstring-doc.noarch: E: incorrect-fsf-address /usr/share/licenses/bstring-doc/gpl.txt

[rdmark]

no problem, I know the pain of fighting with these linters (although lintian doesn't complain about this particular one)

here's a PR that brings over the latest plain text version from gnu.org: #233

the reason we ended up with an older verbiage is because I decided to bring the original author's copies over, which in hindsight was misguided