Fix extension handling

certs/monitor.go

 	for _, f := range files {
 		ext := path.Ext(f.Name())
 		base := path.Base(f.Name())
+		base = base[:len(base)-len(ext)]
 		c.logger.Debugf("File %s has extension %s, base name %s", f.Name(), ext, base)
-		if ext == "pem" {
+		if ext == ".pem" {
 			prefix := strings.Split(base, "-")[0]
 			added := maybeAddPart(&cert, prefix, path.Join(dir, f.Name()))
 			c.logger.Debugf("\tFile prefix is %s, added status %s", prefix, added)