Bump version to make possible add the job to database

Signed-off-by: Vitor Mattos <vitor@php.rio>

appinfo/info.xml

@@ -16,7 +16,7 @@ And in the works for the [coming versions](https://github.com/nextcloud/spreed/m
 
 	]]></description>
 
-	<version>15.0.0-dev.5</version>
+	<version>15.0.0-dev.6</version>
 	<licence>agpl</licence>
 
 	<author>Aleksandra Lazarević</author>