Won't work with libsass >= 3.5

[lolmaus]

Yesterday (April 20), libsass 3.3.3 was released.

https://github.com/sass/libsass/releases
https://github.com/sass/node-sass/releases

Now sass-config-manager crashes with:

File: /path/to/project/node_modules/sass-config-manager/sass/_sass-config-manager.scss (357)
Undefined variable: "$sass-config-namespace"

It seems that it's now illegal to define variables inside an if clause.

To avoid the if clause, we could split the lib into two files: global and local. A user will have a choice which one to import.

[prisis]

Hey @lolmaus,

i will check it the evening and add a fix for it.

Or you like to make a pull request :)