phpPackages.composer: Add unzip to path

Unzip is used by composer to install dependencies etc. If it's not
there it defaults to using PHP's built in zip functions. But they are
slower and composer complains to the user if this happens.

pkgs/top-level/php-packages.nix

@@ -269,7 +269,8 @@ let
       mkdir -p $out/bin
       install -D $src $out/libexec/composer/composer.phar
       makeWrapper ${php}/bin/php $out/bin/composer \
-        --add-flags "$out/libexec/composer/composer.phar"
+        --add-flags "$out/libexec/composer/composer.phar" \
+        --prefix PATH : ${pkgs.lib.makeBinPath [ pkgs.unzip ]}
     '';
 
     meta = with pkgs.lib; {