doc: Fix error for escape sequences in string literals

	Backslash goes first in escape sequences, so it must be
	"any other character following a backslash is interpreted as ...",
	while the doc says "...followed by...".

	Author: Marcus Stollsteimer <sto.mar@web.de>
	[ruby-core:79418] [Bug #13190]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@57895 b2dd03c8-39d4-4d8f-98ff-823fe69b080e