Exception code ranges below 400 should be cast to 500

- Fixes weierophinney/problem-details#3

Author: weierophinney

src/CommonProblemDetails.php

@@ -116,7 +116,7 @@ public static function createFromThrowable(
 
     private static function normalizeStatus(int $status) : int
     {
-        if ($status < 100 || $status > 599) {
+        if ($status < 400 || $status > 599) {
             return 500;
         }
 

test/ProblemDetailsJsonResponseTest.php

@@ -80,6 +80,7 @@ public function outOfRangeStatusCodes()
     {
         return [
             99       => [99],
+            399      => [399],
             600      => [600],
             0        => [0],
             'string' => ['string'],

test/ProblemDetailsXmlResponseTest.php

@@ -80,6 +80,7 @@ public function outOfRangeStatusCodes()
     {
         return [
             99       => [99],
+            399      => [399],
             600      => [600],
             0        => [0],
             'string' => ['string'],