Error during rultor merge

See #1288, release log:

• 51ea389 by @rultor: Merge branch '__rultor'
• 015da05 by @paulodamaso: Merge pull request #1289 from ...
• b465ffe by @paulodamaso: For #1288: fixes for no-rdoc a...
• f3635ad by @fanifieiev: (#1259) Fixed qulice violation...
• bf07fc2 by @fanifieiev: (#1259) Documentation about so...
• a330a20 by @fanifieiev: (#1259) One more test for Sort...
• 4126b7e by @fanifieiev: (#1259) Sorted Set with custom...
• 45b9990 by @paulodamaso: For #1285: updating rultor ima...
• d756bdd by @rultor: Merge branch '__rultor'
• c941b2d by @rultor: Merge branch '__rultor'
• 2f52b54 by @victornoel: (#1185) List Envelope is just ...
• b54cae4 by @victornoel: (#1239) Add extra tests for He...
• 8bbef90 by @victornoel: (#1239) HeadInput is renamed t...
• 63b14f9 by @paulodamaso: For #1281:Correction of year v...
• 1fb3261 by @yegor256: Up to 2020, Happy New Year!
• 90ed098 by @victornoel: (#1236) Immutable decorators a...
• 506a574 by @rultor: Merge branch '__rultor'
• 7c165bf by @iakunin: (#1000) Created puzzle for Rep...
• 909110e by @iakunin: (#1000) Code-review fixes
• b630ba4 by @iakunin: (#1000) Code-review fixes
• and 38 more...

Released by Rultor 1.68.9, see build log