Update call-seq of ARGF.read_nonblock

ARGF.read_nonblock supports `exception: false' like IO#read_nonblock
since 2.3.0.
[Feature #11358]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60401 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -11856,8 +11856,8 @@ argf_readpartial(int argc, VALUE *argv, VALUE argf)
 
 /*
  *  call-seq:
- *     ARGF.read_nonblock(maxlen)              -> string
- *     ARGF.read_nonblock(maxlen, outbuf)      -> outbuf
+ *     ARGF.read_nonblock(maxlen[, options])              -> string
+ *     ARGF.read_nonblock(maxlen, outbuf[, options])      -> outbuf
  *
  *  Reads at most _maxlen_ bytes from the ARGF stream in non-blocking mode.
  */