easy-rsa requires bc package

Description:

When running easy-rsa it looks for bc command.

Same can be confirmed via this line which looks for existence of bc.

https://github.com/OpenVPN/easy-rsa/blob/master/easyrsa3/easyrsa#L2998

Additional info:

I personally do not know what it really does but it is needed for some kind of serial number for inline file.

So better to include it as dependency.

• package version(s): openvpn 2.6.12-1