Use vndr instead of godep.

Signed-off-by: Lantao Liu <lantaol@google.com>

vendor/github.com/docker/docker/pkg/README.md

@@ -0,0 +1,11 @@
+pkg/ is a collection of utility packages used by the Docker project without being specific to its internals.
+
+Utility packages are kept separate from the docker core codebase to keep it as small and concise as possible.
+If some utilities grow larger and their APIs stabilize, they may be moved to their own repository under the
+Docker organization, to facilitate re-use by other projects. However that is not the priority.
+
+The directory `pkg` is named after the same directory in the camlistore project. Since Brad is a core
+Go maintainer, we thought it made sense to copy his methods for organizing Go code :) Thanks Brad!
+
+Because utility packages are small and neatly separated from the rest of the codebase, they are a good
+place to start for aspiring maintainers and contributors. Get in touch if you want to help maintain them!

vendor/github.com/docker/docker/pkg/signal/trap.go

@@ -11,8 +11,8 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/Sirupsen/logrus"
 	"github.com/pkg/errors"
-	"github.com/sirupsen/logrus"
 )
 
 // Trap sets up a simplified signal "trap", appropriate for common