fix: urlencode version in RenameFilename

As per Mircea's comment on [#44 (comment)](#44 (comment)):

    I've also now noticed that RenameVersion is also not correctly
    escaping the filename, it's only escaping the mod's name, and
    not the version, which is what causes mods that use build
    metadata in the version (+build.1234) to fail, so that one
    should need a similar fix of encoding the filename.

storage/storage.go

@@ -276,7 +276,7 @@ func RenameVersion(ctx context.Context, modID string, name string, versionID str
 		return false, ""
 	}
 
-	return true, fmt.Sprintf("/mods/%s/%s.smod", modID, EncodeName(cleanName)+"-"+version)
+	return true, fmt.Sprintf("/mods/%s/%s.smod", modID, EncodeName(cleanName + "-" + version))
 }
 
 func DeleteMod(ctx context.Context, modID string, name string, versionID string) bool {