composer.json中的特定提交版本产生奇怪的需求

我正在尝试使用一个旧的PHP源代码。 composer.json 包含:

{
    "minimum-stability": "dev",
    "name": "symfony/framework-standard-edition",
    "description": "The \"Symfony Standard Edition\" distribution",
    "autoload": {
        "psr-0": { "": "src/" }
    },
    "require": {
        "php": ">=5.3.3",
        "symfony/symfony": "v2.2.4",
        [...]
        "friendsofsymfony/user-bundle": "v1.3.1",
        "doctrine/data-fixtures" : "dev-master#b4a135c",
        [...]

但当我奔跑 php composer.phar install 我得到:

  Problem 1
    - Installation request for doctrine/data-fixtures dev-master#b4a135c -> satisfiable by doctrine/data-fixtures[dev-master].
    - doctrine/data-fixtures dev-master requires php ^7.1 -> your PHP version (5.6.37) does not satisfy that requirement.

doctrine/data-fixtures 此提交的要求是 here .

为什么作曲家要谈论PHP ^7.1 ?如何真正使用版本 b4a135c 这个包裹的?