>= ruby 2.4.0 warns that constant ::Fixnum is deprecated

[dshorthouse]

https://github.com/sckott/serrano/blob/e778042b373d16e6afd1e50e9867e5744574fed9/lib/serrano/request_cursor.rb#L65

Could this instead be:

if !self.cursor_max.kind_of?(Integer)
  raise "cursor_max must be of class int"
end

[sckott]

thanks @dshorthouse will have a look