Config file with duplicated keys passes validation

[Unisay]

Setup:

1. config file with duplicate key/value pairs.
2. latest confcrypt version

Actual behavior:

• confcrypt aws validate file.econf outputs no validation erros.
• confcrypt aws edit ... removes duplicated keys.

Expected behavior:

• confcrypt aws validate file.econf reports duplicated keys.
• confcrypt aws edit ... validates file prior to editing.