IPAddr#mask method accepts arguments other than integers.

IPAddr#mask method expects an integer argument, but it accepts non-integer values (such as floats or arrays) if passed.

ip = IPAddr.new('1.2.3.4')

p ip.mask(0.1)
# => #<IPAddr: IPv4:0.0.0.0/128.0.0.0>
p ip.mask(1.2)
# => #<IPAddr: IPv4:0.0.0.0/192.0.0.0>
p ip.mask(11.3)
# => #<IPAddr: IPv4:1.0.0.0/255.240.0.0>
p ip.mask([])
# => `mask!': undefined method `<' for []:Array (NoMethodError)

So, I think it is better to restrict the arguments of this method to integers and throw an exception if they are not integers.
Like this.

ip = IPAddr.new('1.2.3.4')

p ip.mask(0.1)
# => `mask!': invalid mask 0.1 (IPAddr::InvalidPrefixError)

I'm currently implementing this improvement and want to submit a pull request as a contribute to this repo.
Would this be acceptable?

IPAddr#mask メソッドから始め、issue の float と array の例を再現してください。整数でない引数が IPAddr::InvalidPrefixError を発生させ、整数マスクが引き続き期待どおりに動作すれば、変更は完了です。