Support cancancan 2.2

[jeremyyap]

Close #3

Disable ActiveRecord5Adapter introduced in CanCanCommunity/cancancan#479

[houndci-bot]

Some files could not be reviewed due to errors:

.rubocop.yml: Style/FileName has the wrong namespace - should be Naming

.rubocop.yml: Style/FileName has the wrong namespace - should be Naming
.rubocop.yml: Style/AccessorMethodName has the wrong namespace - should be Naming
.rubocop.yml: Style/DotPosition has the wrong namespace - should be Layout
.rubocop.yml: Style/IndentHash has the wrong namespace - should be Layout
Error: The `Style/TrailingCommaInLiteral` cop no longer exists. Please use `Style/TrailingCommaInArrayLiteral` and/or `Style/TrailingCommaInHashLiteral` instead.
(obsolete configuration found in .rubocop.yml, please update it)
obsolete parameter MaxLineLength (for Style/IfUnlessModifier) found in .rubocop.yml
`Style/IfUnlessModifier: MaxLineLength` has been removed. Use `Metrics/LineLength: Max` instead
obsolete parameter MaxLineLength (for Style/WhileUntilModifier) found in .rubocop.yml
`Style/WhileUntilModifier: MaxLineLength` has been removed. Use `Metrics/LineLength: Max` instead

[coveralls]

Pull Request Test Coverage Report for Build 39

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.7%) to 95.376%

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Totals
Change from base Build 9:	0.7%
Covered Lines:	165
Relevant Lines:	173

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💛 - Coveralls