Return type PHP 7.1

[Gauss23]

Hello,

the languageserver is crashing when defining a function with a return type of "?string" instead of "string". "?string" means it´s a string or null. Same for "?int" etc.

It crashes with:

[Error - 17:54:56] Request textDocument/hover failed.
  Message: ErrorException: Object of class PhpParser\Node\NullableType could not be converted to string in XXXXXXX\.vscode\extensions\felixfbecker.php-intellisense-1.2.1\vendor\felixfbecker\language-server\src\DefinitionResolver.php:792
Stack trace:

Best regards and thank you for the excellent work!

[felixfbecker]

felixfbecker/php-language-server#292
felixfbecker/php-language-server#290