Odd/nonsensical error "Json.php - Syntax error" on simple run.

Using PHPStan 0.12.25 or 0.12.27
```
$ vendor/bin/phpstan analyse 

In Json.php line 45:
                
  Syntax error  
                
```
Empty, skeleton project, no `json.php` or `Json.php` anywhere in the directory, no `phpstan.neon`. 
