Merge pull request bcrypt-ruby#172 from codahale/gem_3-1-12-rc

RC for 3.1.12 release

RC for 3.1.12 release

With support for 2.3-2.5 on Windows and Fedora 28 with libxcrypt

Version bump to 3.1.11

Version bump to 3.1.10

Version bump to 3.1.9

Version bump to 3.1.8

Fixes bcrypt-ruby#102

Version bump to 3.1.7

Version bump to 3.1.6

JRuby in 1.8 mode doesn't play nicely with rdoc v4

Version bump for 3.1.1 official release