According to the documentation "deployer" element can not contain "deployables" child element. To make things work you should place "deployables" under "configuration" element
<configuration>
<container>
[...]
</container>
<configuration>
<type>standalone</type>
[...]
</configuration>
<deployables>
<deployable>
<groupId>my.war.groupId</groupId>
<artifactId>my-war</artifactId>
<type>war</type>
</deployable>
</deployables>
</configuration>