canonicalise problem file path

Author: AydinHassan

src/Exception/ProblemFileDoesNotExistException.php

@@ -8,6 +8,9 @@ class ProblemFileDoesNotExistException extends \RuntimeException
 {
     public static function fromFile(string $file): self
     {
-        return new self("Exercise problem file: '$file' does not exist or is not readable");
+        return new self(sprintf(
+            'Exercise problem file: "%s" does not exist or is not readable',
+            canonicalise_path($file)
+        ));
     }
 }