vendor: Update certmagic; fix #2400

vendor/github.com/mholt/certmagic/config.go

@@ -289,6 +289,10 @@ func (cfg *Config) ObtainCert(name string, interactive bool) error {
 		return nil
 	}
 
+	if cfg.storageHasCertResources(name) {
+		return nil
+	}
+
 	client, err := cfg.newACMEClient(interactive)
 	if err != nil {
 		return err

vendor/manifest

@@ -138,7 +138,7 @@
 			"importpath": "github.com/mholt/certmagic",
 			"repository": "https://github.com/mholt/certmagic",
 			"vcs": "git",
-			"revision": "707b20497ed70e559300ae4e91c6fd7db973fffc",
+			"revision": "01ffe8b3c7d611483ef936e90845329709721127",
 			"branch": "master",
 			"notests": true
 		},