Fix for when custom_path is not defined.  on Windows this was causing th...

...e cookbook to not be bumped correctly, and was failing without an exception

Sample output pre change:
C:\code\Internal\cookbooks\eis\sys_win_base>knife spork bump sys_win_base -o "./../"
exit
I ran

Post Change:
C:\code\Internal\cookbooks\eis\sys_win_base>knife spork bump sys_win_base -o "./../"
Successfully bumped sys_win_base to v0.2.5!