Switched to Perl local::lib for local compilation.

Taken from upstream Slic3r, thanks @alexrj.

t/retraction.t

@@ -5,6 +5,7 @@ use warnings;
 BEGIN {
     use FindBin;
     use lib "$FindBin::Bin/../lib";
+    use local::lib "$FindBin::Bin/../local-lib";
 }
 
 use List::Util qw(any);