Back port 0.14.x case-sensitivity fix for RateLimit handling to 0.13.x

src/shared/http/CurlHttpClient.php

@@ -85,7 +85,7 @@ public function handleHeaderInput($ch, string $line): int {
         if ($header === 'Etag') {
             $this->etag = new ETag($value);
         } else if (preg_match('/^(X-)?RateLimit-(.*)$/i', $header, $matches) === 1) {
-            $this->rateLimitHeaders[$matches[2]] = $value;
+            $this->rateLimitHeaders[\ucfirst(\strtolower($matches[2]))] = $value;
         }
 
         return \mb_strlen($line);