fix array to string conversion notices

[nikolashermann]

fixes notice:

PHP Version: 5.6.4-1~dotdeb.1 (Linux)
PHPDox Version: c4f9402-dirty
ErrorException: E_NOTICE 
Location: .../vendor/theseer/phpdox/src/collector/project/AbstractUnitObject.php (Line 344)

Array to string conversion

#0 .../vendor/theseer/phpdox/src/collector/project/AbstractUnitObject.php(344): sprintf()
#1 .../vendor/theseer/phpdox/src/collector/InheritanceResolver.php(148): TheSeer\phpDox\Collector\AbstractUnitObject->markDependencyAsUnresolved()
#2 .../vendor/theseer/phpdox/src/collector/InheritanceResolver.php(165): TheSeer\phpDox\Collector\InheritanceResolver->addUnresolved()
#3 .../vendor/theseer/phpdox/src/collector/InheritanceResolver.php(92): TheSeer\phpDox\Collector\InheritanceResolver->processExtends()
#4 .../vendor/theseer/phpdox/src/Application.php(145): TheSeer\phpDox\Collector\InheritanceResolver->resolve()
#5 .../vendor/theseer/phpdox/src/CLI.php(156): TheSeer\phpDox\Application->runCollector()
#6 .../vendor/theseer/phpdox/phpdox(65): TheSeer\phpDox\CLI->run()

[theseer]

Nice catch, thank you.