AndroidManifestEditor: Fix versionCode being limited

The android documentation does not require a minimum value of 1,
but suggest that "Typically, you would release the first version
of your application with versionCode set to 1". Thus keep the
minimum of 1. A maximum value is not specified.

Task-number: QTCREATORBUG-12668
Change-Id: I6bfb0a534661af82b6fcfe5667d9224893707e41
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>