Update a few dependencies

github.com/go-openapi/*
github.com/asaskevich/govalidator

vendor/github.com/go-openapi/swag/post_go18.go

@@ -0,0 +1,9 @@
+// +build go1.8
+
+package swag
+
+import "net/url"
+
+func pathUnescape(path string) (string, error) {
+	return url.PathUnescape(path)
+}