[ticket/12302] Updated composer.phar to 1.0.0-alpha8

wget -N https://getcomposer.org/download/1.0.0-alpha8/composer.phar

PHPBB3-12302
[ticket/12302] Added `--no-dev` to composer call in build.xml

PHPBB3-12302
Merge pull request #2183 from s9e/ticket/12302

Upgrade all composer.phar to 1.0.0-alpha8

* s9e/ticket/12302:
  [ticket/12302] Added `--no-dev` to composer call in build.xml
  [ticket/12302] Updated composer.phar to 1.0.0-alpha8