Update vendoring and fix Windows build

We were missing one repo needed for Windows; but we have also not deleted
a bunch of vendored code that we are no longer using.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

vendor/github.com/Azure/go-ansiterm/context.go

@@ -0,0 +1,7 @@
+package ansiterm
+
+type ansiContext struct {
+	currentChar byte
+	paramBuffer []byte
+	interBuffer []byte
+}