Fix error on ruby 2.5

[Jeremy Evans <code@jeremyevans.net>]

Example code:

require 'socket'
require 'kgio'
addr = Socket.pack_sockaddr_in(80, 'www')
socket = Kgio::Socket.connect(addr)
buf = String.new(:capacity=>16384); nil
socket.kgio_read!(16384, buf)

Result on ruby 2.5:

TypeError: can't convert FalseClass into time interval

Cause:

Misuse of rb_funcall.  Not sure why ruby 2.5 is pickier than previous
versions.

Noticed when testing unicorn with ruby 2.5.

Fix:

--- ext/kgio/wait.c.orig
+++ ext/kgio/wait.c
@@ -92,12 +92,12 @@ static VALUE kgio_wait_writable(int argc, VALUE *argv,
 
 VALUE kgio_call_wait_writable(VALUE io)
 {
-	return rb_funcall(io, id_wait_wr, 0, 0);
+	return rb_funcall(io, id_wait_wr, 0);
 }
 
 VALUE kgio_call_wait_readable(VALUE io)
 {
-	return rb_funcall(io, id_wait_rd, 0, 0);
+	return rb_funcall(io, id_wait_rd, 0);
 }
 
 void init_kgio_wait(void)