Doesn't work with bash-3.2.57(1)-release

Getting this error:
```
util/bashpp.sh: line 44: declare: -A: invalid option
```
when executing:
```
util/bashpp.sh -o values.yaml values.yaml.tmpl
```

But it works with bash version `5.0.17(1)-release`.

If the `bashpp` doesn't support some versions of bash - it would be great to note it somewhere or add check into the script.
