tty-prompt: IOError on Windows

Getting this:

`sysread': sysread for buffered IO (IOError)
from C:/Ruby/lib/ruby/gems/2.0.0/gems/tty-prompt-0.7.1/lib/tty/prompt/reader.rb:93
from C:/Ruby/lib/ruby/gems/2.0.0/gems/tty-prompt-0.7.1/lib/tty/prompt/reader.rb:78:in `block (3 levels) in read_keypress'

In reference to https://github.com/kontena/kontena/issues/1401