LengthOf must be a Number

See #519, release log:

• ef4086f by @yegor256: #519 doc
• 9435f29 by @yegor256: Merge branch 'master' of githu...
• 07826a5 by @yegor256: #519 LengthOf is a Number
• 08b0d32 by @yegor256: Merge pull request #517 from j...
• 52b15a8 by @janczer: Fixed typos
• 619d321 by @fabriciofx: #510 HexOf
• ed77721 by @svendiedrichsen: Merge branch 'master' of https...
• 8b5cd5c by @svendiedrichsen: #505 fixing puzzle. the zone i...
• 2c9ef05 by @rultor: Merge branch '__rultor'
• f15a9a3 by @Zefick: removed extra constructors fro...
• e36349a by @rultor: Merge branch '__rultor'

Released by Rultor 1.67, see build log