Correct darwin paths to .dylib

[chee]

.dynlib isn't a thing! also the file format is .\d+.dylib rather than .dylib.\d+ c:

[chee]

This works like this on my macos system, but i did have to install readline with homebrew and then do brew link readline --force.

On macos by default, /usr/lib/libreadline.dylib is a symlink to libedit.3 which is a basket of lols.

So far i haven't run into any problems from programs expecting getting libreadline when they asked for libreadline but i'm sure the --force install is not a recommended path.

The default path to the non-force-linked brew installed libreadline would be /usr/local/Cellar/readline/8.0.0/lib/, so there'd need to be an entry in library-paths for every readline version unless a glob was used.

However, this would be the normal name and location for someone who has downloaded, ./configure'd make'd and sudo make install'd readline themselves on a mac, so I feel this PR is valuable.

I think this should help with #20. 😊