Upgrade to Go1.6, use vendor

Also make sure we're using a more recent version of godep

vendor/github.com/mitchellh/go-homedir/README.md

@@ -0,0 +1,14 @@
+# go-homedir
+
+This is a Go library for detecting the user's home directory without
+the use of cgo, so the library can be used in cross-compilation environments.
+
+Usage is incredibly simple, just call `homedir.Dir()` to get the home directory
+for a user, and `homedir.Expand()` to expand the `~` in a path to the home
+directory.
+
+**Why not just use `os/user`?** The built-in `os/user` package requires
+cgo on Darwin systems. This means that any Go code that uses that package
+cannot cross compile. But 99% of the time the use for `os/user` is just to
+retrieve the home directory, which we can do for the current user without
+cgo. This library does that, enabling cross-compilation.