Composer.lock file into version control.

Written in composer official docs:
"Commit your application's composer.lock (along with composer.json) into version control."
URL>> http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file
Merge pull request #281 from takyam-git/fix/remove_composer_lock_from_gitignore

Composer.lock file into version control.