Use a case insenstive method to check that SHA384 is a supported openssl algorithm

src/Composer/Command/SelfUpdateCommand.php

@@ -220,7 +220,7 @@ TAGSPUBKEY
 
             $pubkeyid = openssl_pkey_get_public($sigFile);
             $algo = defined('OPENSSL_ALGO_SHA384') ? OPENSSL_ALGO_SHA384 : 'SHA384';
-            if (!in_array('SHA384', openssl_get_md_methods())) {
+            if (!in_array('sha384', array_map('strtolower', openssl_get_md_methods()))) {
                 throw new \RuntimeException('SHA384 is not supported by your openssl extension, could not verify the phar file integrity');
             }
             $signature = json_decode($signature, true);