Fix cmake config path on Linux.

[xkszltl]

CMake config files were installed to /usr/local/share/hiredis, which is not recognizable by find_package(). I'm not sure why it was set that way. Given the commit introducing it is for Windows, I keep that behavior consistent there, but fix the rest.

[michael-grunder]

I'm pretty unfamiliar with CMake but this does appear correct. I'll read up a bit on CMake's find_package and then get it merged.

[xkszltl]

Emmm....Actually after double checking I might be wrong. /usr/local/share/hiredis could be supported as well. Originally I saw it after packaging into rpm and think that doesn't look right, probably because rarely anyone uses that.

[michael-grunder]

So can this be closed then?

[xkszltl]

Up to you, but I would recommend to merge. This PR fixed a "package not found" issue, although I'm not sure about the root cause because either way should be OK based on the doc.

[michael-grunder]

Merged, thanks!

@chayim Thanks for the help!