Don't compress the archive made from git's output.

Commit 894d4a23fba made BuildFile use TarSum, which doesn't support
compressed tar archives.
This breaks builds from git url, which compressed it with bzip2.
Instead, just pass it uncompressed.

Docker-DCO-1.0-Signed-off-by: Paul Lietar <paul@lietar.net> (github: plietar)
diff --git a/AUTHORS b/AUTHORS
index 1ff9b8d..35cfc68 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -148,6 +148,7 @@
 Pascal Borreli <pascal@borreli.com>
 Paul Bowsher <pbowsher@globalpersonals.co.uk>
 Paul Hammond <paul@paulhammond.org>
+Paul Liétar <paul@lietar.net>
 Paul Nasrat <pnasrat@gmail.com>
 Phil Spitler <pspitler@gmail.com>
 Piotr Bogdan <ppbogdan@gmail.com>
diff --git a/api.go b/api.go
index 972abbf..9fe9bc7 100644
--- a/api.go
+++ b/api.go
@@ -929,7 +929,7 @@
 			return fmt.Errorf("Error trying to use git: %s (%s)", err, output)
 		}
 
-		c, err := archive.Tar(root, archive.Bzip2)
+		c, err := archive.Tar(root, archive.Uncompressed)
 		if err != nil {
 			return err
 		}