Raise correct error message when create cache proxy with absent cache type

[ar0ne]

What do these changes do?

I got this error message when tried to use aiocache with redis.

assert issubclass(cache_class, BaseCache)
TypeError: issubclass() arg 1 must be a class

Basically, I wasn't sure which dependency is missed, because I assumed pip install aiocache should install all required. Also this command from readme doesn't work for me.

>> pip install aiocache[redis]
zsh: no matches found: aiocache[redis]

Are there changes in behavior for the user?

Related issue number

Fixes #539

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes

[Dreamsorcerer]

zsh: no matches found: aiocache[redis]
Looks like a shell error, maybe try 'aiocache[redis]'? I assume your shell is trying to do something with the brackets.

[Dreamsorcerer]

I'm planning to remove the whole factory thing from v1, which will avoid silly errors like this completely. If you can retarget the PR to the 0.12 branch though, I'll merge this in for now.

[ar0ne]

recreated #795