CWD causes the script to bail when it's not set

`fileObj.orig.cwd` can returned undefined which will kill the `path.relative` call with a warning. This gives it a default empty string to base the relative off of.

tasks/scp.js

@@ -78,7 +78,7 @@ module.exports = function(grunt) {
           filename = filepath;
           filepath = path.join(fileObj.cwd, filepath);
         } else {
-          filename = path.relative(fileObj.orig.cwd, filepath);
+          filename = path.relative(fileObj.orig.cwd || '', filepath);
         }
         destfile = path.join(fileObj.dest, filename);
         client.upload(filepath, destfile, cb);