Update slevomat/coding-standard requirement from ^5.0 to ^6.0

[dependabot-preview]

Updates the requirements on slevomat/coding-standard to permit the latest version.

Release notes

Sourced from slevomat/coding-standard's releases.

6.0.0

New sniffs

• RequireArrowFunctionSniff: Requires arrow functions
• DisallowArrowFunctionSniff: Disallows arrow functions
• RequireNumericLiteralSeparatorSniff: Requires use of numeric literal separators
• DisallowNumericLiteralSeparatorSniff: Disallows numeric literal separators
• RequireNowdocSniff: Requires nowdoc syntax instead of heredoc when possible
• ReferenceSpacingSniff: Enforces configurable number of spaces after reference
• DisallowReferenceSniff: Disallows references
• RequireExplicitAssertionSniff: Requires assertion via assert() instead of inline documentation comments.
• ParameterTypeHintSniff: Previously part of TypeHintDeclarationSniff
• PropertyTypeHintSniff: Previously part of TypeHintDeclarationSniff
• ReturnTypeHintSniff: Previously part of TypeHintDeclarationSniff
• UselessFunctionDocCommentSniff: Previously part of TypeHintDeclarationSniff
• BlockControlStructureSpacingSniff: Previously part of ControlStructureSpacingSniff
• JumpStatementsSpacingSniff: Previously part of ControlStructureSpacingSniff

Improvements

• PHP 7.4 support
• Arrow functions support
• Array shapes in phpDocs support
• PropertyTypeHintSniff: Support for native type hints
• InlineDocCommentDeclarationSniff: Reports missing related variables or no assigment
• InlineDocCommentDeclarationSniff: Added support for doccomments after variable definition
• InlineDocCommentDeclarationSniff: Added support for list() and short list []
• TrailingArrayCommaSniff: New option enableAfterHeredoc
• DisallowMixedTypeHintSniff: Added suppress support
• UselessParenthesesSniff: Reports more useless parentheses

Fixes

• Fixed support of @method annotation
• InlineDocCommentDeclarationSniff: Check really only inline doccomments
• TrailingCommaInCallSniff: Some calls were not reported
• UselessParenthesesSniff: Fixed false positive
• NamespaceSpacingSniff: Fixed false positive
• UselessSemicolonSniff: Fixed internal error
• TypeNameMatchesFileNameSniff: Files without namespaces should be reported too
• UseSpacingSniff: Don't report errors for use statements with comments right before or after
• UselessVariableSniff: Fixed false positive
• UselessParameterDefaultValueSniff: Fixed false positive
• UnusedPrivateElementsSniff: Fixed false positive
• UnusedUsesSniff: Better handle php open tags (thanks to @​donatj)
• RequireCombinedAssignmentOperatorSniff: Fixed false positive
• UselessInheritDocCommentSniff: Fixed internal error
• RequireShortTernaryOperatorSniff: Fix token overrun (thanks to @​donatj)
• Fix compatibility with non-Composer installs of PHPCS (thanks to @​jrfnl)

... (truncated)

Commits

• 85e3329 UselessFunctionDocCommentSniff: Fixed internal error
• dc5a270 RequireExplicitAssertionSniff: Fixed internal error
• 8f7a1de RequireArrowFunctionSniff: Fixed fixer
• db3b3b5 Updated dependencies
• 26d37c7 Fixed tests
• d26de94 Added RequireArrowFunctionSniff
• 1543263 PropertyTypeHintSniff: Improved fixer for nullable properties
• 26a509a Fixed PropertyHelper::findTypeHint()
• da11950 PropertyTypeHintSniff: No more invalid code after fixing
• ae4daff Fix travis error when running php 7.1 and php 7.2
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #50.