Low priority bug : `cprop.tool/map->env-file` doesn't support dotted namespaced keys

```clojure
(cprop.tools/map->env-file {:composite.key/namespaced 43})
=> "/tmp/cprops-1629906434989-8080623925560935467.tmp"
(println (slurp *1))
export NAMESPACED=43
=> nil
```

The content of the file should be : 
```
export COMPOSITE.KEY___NAMESPACED=43
```
