Fix an issue where on POSIX-like filesystems first '/' in absolute file path would be lost.

[gordeevbr]

Greetings!

I have stumbled across the same issue as #42 and I think I have found the cause.

Using path.join('./', context, importThisFile) in the file reading function for #import directive of mock files just so happens to be removing the first '/' from the absolute file path on POSIX-like file systems. So instead of /user/something/whatever/file.json one would get user/something/whatever/file.json which would cause an error.

Since this issue seems to be relatively not very popular I guess it only happens under some circumstances. It appears to be that using just path.join(context, importThisFile) will solve this problem. I'm not sure why path.join('./', context, importThisFile) was used before since "context" variable is assigned path.parse(file).dir + '/' in the code and NodeJS docks say it will evaluate to an absolute directory path on both file systems anyway. Please correct me if I'm wrong here.

Please review this and merge if necessary.

[gordeevbr]

P.S. all tests still pass.

[odino]

Thanks!