[CI] Try to make composer run

Dockerfile.linux.amd64

@@ -6,19 +6,19 @@ RUN set -e && ln -sf bash /bin/sh
 RUN set -e \
       && apt -y update \
       && apt -y upgrade \
-      && apt -y install --no-install-recommends --no-install-suggests ca-certificates git \
+      && apt -y install --no-install-recommends --no-install-suggests ca-certificates composer git \
       && apt -y autoremove \
       && apt clean \
       && rm -rf /var/lib/apt/lists/*
 
 # install plugins using composer
-RUN set -e \
-      /usr/bin/composer \
-        --working-dir=/usr/src/roundcubemail/ \
-        --prefer-dist \
-        --prefer-stable \
-        --update-no-dev \
-        --no-interaction \
-        --optimize-autoloader \
-        require \
-          johndoh/contextmenu
+RUN set -e && /usr/bin/composer \
+      --working-dir=/usr/src/roundcubemail/ \
+      --prefer-dist \
+      --prefer-stable \
+      --update-no-dev \
+      --no-interaction \
+      --optimize-autoloader \
+      --quiet \
+      require \
+        johndoh/contextmenu