IPVanish support (#475)

- Fix #410 and #416

internal/updater/providers/ipvanish/string.go

@@ -0,0 +1,14 @@
+package ipvanish
+
+import "github.com/qdm12/gluetun/internal/models"
+
+func Stringify(servers []models.IpvanishServer) (s string) {
+	s = "func IpvanishServers() []models.IpvanishServer {\n"
+	s += "	return []models.IpvanishServer{\n"
+	for _, server := range servers {
+		s += "		" + server.String() + ",\n"
+	}
+	s += "	}\n"
+	s += "}"
+	return s
+}