vendor: add github.com/ncw/dropbox-sdk-go-unofficial and remove github.com/stacktic/dropbox

In due course this will become github.com/dropbox/dropbox-sdk-go-unofficial
when the fate of https://github.com/dropbox/dropbox-sdk-go-unofficial/pull/14
has been decided.

Gopkg.lock

@@ -1,4 +1,4 @@
-memo = "73fcf12d2ac21c6ada1f1c0d63c636506e4f576081d0509e38d53086f6f67447"
+memo = "e0227ed773a9f6c56d1bfac9de1d87c2a74ce142e418b661b74931d2e2b20945"
 
 [[projects]]
   branch = "master"
@@ -96,6 +96,12 @@ memo = "73fcf12d2ac21c6ada1f1c0d63c636506e4f576081d0509e38d53086f6f67447"
   packages = ["."]
   revision = "2788f0dbd16903de03cb8186e5c7d97b69ad387b"
 
+[[projects]]
+  branch = "master"
+  name = "github.com/ncw/dropbox-sdk-go-unofficial"
+  packages = ["dropbox","dropbox/async","dropbox/files","dropbox/properties"]
+  revision = "5d9f46f9862ae5f65e264e178de6ce2c41a32d40"
+
 [[projects]]
   branch = "master"
   name = "github.com/ncw/go-acd"
@@ -162,12 +168,6 @@ memo = "73fcf12d2ac21c6ada1f1c0d63c636506e4f576081d0509e38d53086f6f67447"
   packages = ["."]
   revision = "e57e3eeb33f795204c1ca35f56c44f83227c6e66"
 
-[[projects]]
-  branch = "master"
-  name = "github.com/stacktic/dropbox"
-  packages = ["."]
-  revision = "58f839b21094d5e0af7caf613599830589233d20"
-
 [[projects]]
   branch = "master"
   name = "github.com/stretchr/testify"