Bump phpstan to 0.12

[phil-davis]

and enhance some PHPdoc to keep phpstan happy.

phpstan was fussing about:

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  Line   functions.php                                                          
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  192    Function Sabre\Uri\parse() return type has no value type specified in  
         iterable type array.                                                   
         💡 Consider adding something like array<Foo> to the                     
         PHPDoc.                                                                
         You can turn off this check by setting                                 
         checkMissingIterableValueType: false in your                           
         /home/travis/build/sabre-io/uri/phpstan.neon.                          

  232    Function Sabre\Uri\build() has parameter $parts with no value type     
         specified in iterable type array.                                      
         m💡 Consider adding something like array<Foo> to the                     
         PHPDoc.                                                                
         You can turn off this check by setting                                 
         checkMissingIterableValueType: false in your                           
         /home/travis/build/sabre-io/uri/phpstan.neon.                          

  288    Function Sabre\Uri\split() return type has no value type specified in  
         iterable type array.                                                   

         💡 Consider adding something like array<Foo> to the                     
         PHPDoc.                                                                
         You can turn off this check by setting                                 
         checkMissingIterableValueType: false in your                           
         /home/travis/build/sabre-io/uri/phpstan.neon.                          

  314    Function Sabre\Uri\_parse_fallback() return type has no value type     

         specified in iterable type array.                                      
         💡 Consider adding something like array<Foo> to the                     
         PHPDoc.                                                                
         You can turn off this check by setting                                 
         checkMissingIterableValueType: false in your                           
         /home/travis/build/sabre-io/uri/phpstan.neon.                          
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 [ERROR] Found 4 errors