Revert "Rollback to released version numbers of stringio and strscan"

	This reverts commit 6a79e53823e328281b9e9eee53cd141af28f8548.

	[ruby/strscan] StringScanner#captures: Return nil not "" for unmached capture (https://github.com/ruby/strscan/pull/72)

	fix https://github.com/ruby/strscan/issues/70
	If there is no substring matching the group (s[3]), the behavior is
	different.

	If there is no substring matching the group, the corresponding element
	(s[3]) should be nil.

	```
	s = StringScanner.new('foobarbaz') #=> #<StringScanner 0/9 @ "fooba...">
	s.scan /(foo)(bar)(BAZ)?/  #=> "foobar"
	s[0]           #=> "foobar"
	s[1]           #=> "foo"
	s[2]           #=> "bar"
	s[3]           #=> nil
	s.captures #=> ["foo", "bar", ""]
	s.captures.compact #=> ["foo", "bar", ""]
	```

	```
	s = StringScanner.new('foobarbaz') #=> #<StringScanner 0/9 @ "fooba...">
	s.scan /(foo)(bar)(BAZ)?/  #=> "foobar"
	s[0]           #=> "foobar"
	s[1]           #=> "foo"
	s[2]           #=> "bar"
	s[3]           #=> nil
	s.captures #=> ["foo", "bar", nil]
	s.captures.compact #=> ["foo", "bar"]
	```

	https://docs.ruby-lang.org/ja/latest/method/MatchData/i/captures.html
	```
	/(foo)(bar)(BAZ)?/ =~ "foobarbaz" #=> 0
	$~.to_a        #=> ["foobar", "foo", "bar", nil]
	$~.captures #=> ["foo", "bar", nil]
	$~.captures.compact #=> ["foo", "bar"]
	```

	* StringScanner#captures is not yet documented.
	https://docs.ruby-lang.org/ja/latest/class/StringScanner.html

	https://github.com/ruby/strscan/commit/1fbfdd3c6f

	[ruby/strscan] Bump version

	https://github.com/ruby/strscan/commit/d6f97ec102

https://github.com/ruby/strscan/commit/1b3393be05

[ci skip]

rb_reg_onig_match performs preparation, error handling, and cleanup for
matching a regex against a string. This reduces repetitive code and
removes the need for StringScanner to access internal data of regex.

Syncs commit ruby/strscan@76b377a5d875ec77282d9319d62d8f24fe283b40.

https://github.com/ruby/strscan/commit/681cde0f27

(https://github.com/ruby/strscan/pull/49)

The doc of `rest?` was unclear about return value. This commit adds the
return value to the doc.

https://github.com/ruby/strscan/commit/3ada12613d