Sanity check for NumberFormatter when intl is not installed (#91)

* added sanity check for NumberFormatter class when intl extension is not installed

* Update MetricSuffix.php

* Update BinarySuffix.php

Author: thunderer

src/Coduo/PHPHumanizer/String/BinarySuffix.php

@@ -39,6 +39,10 @@ final class BinarySuffix
      */
     public function __construct($number, $locale = 'en', $precision = null)
     {
+        if (!\class_exists('NumberFormatter')) {
+            throw new \RuntimeException('Binary suffix converter requires intl extension!');
+        }
+
         if (!\is_numeric($number)) {
             throw new \InvalidArgumentException('Binary suffix converter accept only numeric values.');
         }

src/Coduo/PHPHumanizer/String/MetricSuffix.php

@@ -38,6 +38,10 @@ final class MetricSuffix
      */
     public function __construct($number, $locale = 'en')
     {
+        if (!\class_exists('NumberFormatter')) {
+            throw new \RuntimeException('Metric suffix converter requires intl extension!');
+        }
+
         if (!\is_numeric($number)) {
             throw new \InvalidArgumentException('Metric suffix converter accept only numeric values.');
         }