Update adapter-redis.gemspec

Support for the latest version of the redis gem, which is thread-safe by default.
Update adapter-redis.gemspec

Updated to use the latest version of adapter gem. (0.7.0), instead of 0.5.1.
Updating gems to their up-to-date versions.
Updated gems.
Replacing specs with working ones from adapter. They require updating to work with this adapter.
Bumping the version.