使用 Dockerfile 安装 Composer 失败

以下是用来构建PHP镜像的Dockerfile内容，基于官方镜像php:7.2-fpm-alpine

镜像可以构建成功，PHP的扩展也都安装成功了，但是composer没有安装上

FROM php:7.2-fpm-alpine

RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories

RUN apk add --no-cache --virtual .build-deps \
        $PHPIZE_DEPS \
        curl-dev \
        imagemagick-dev \
        libtool \
        libxml2-dev \
    && apk add --no-cache \
        curl \
        git \
        imagemagick \
        mysql-client \
    && pecl install imagick \
    && docker-php-ext-enable imagick \
    && docker-php-ext-install \
        curl \
        iconv \
        mbstring \
        pdo \
        pdo_mysql \
        pdo_pgsql \
        pdo_sqlite \
        pcntl \
        tokenizer \
        xml \
        zip \
        openssl \
    && apk del -f .build-deps

RUN curl -s https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin/ --filename=composer

RUN composer config -g repo.packagist composer https://mirrors.aliyun.com/composer/