typo in regex

See #16, release log:

• 76bb4fc by @yegor256: #16 comment
• b58f584 by @yegor256: #16 fmt
• 96f74b6 by @yegor256: #16 fmt
• f17fe43 by @yegor256: #16 fmt
• aa32990 by @yegor256: #16 typo
• fa6a8d3 by @yegor256: #16 fixed

Released by Rultor 1.75.1, see build log