reason: fix save path for when GOPATH contains a list of multiple paths.

The following error was triggered before:

main.HeroAction (reason.go:176): error: open /home/u/goget:/home/u/Desktop/go/src/github.com/karlek/reason/debug.save: no such file or directory
Merge pull request #1 from mewmew/master

reason: fix save path for when GOPATH contains a list of multiple paths.