upgrading composer

Signed-off-by: Maxence Lange <maxence@artificial-owl.com>

composer.lock

@@ -1,7 +1,7 @@
 {
     "_readme": [
         "This file locks the dependencies of your project to a known state",
-        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
     "content-hash": "2c21b8c338f3d2f929f349df19edbc0e",