Update composer.json

According to the README.md the extension requires PHPUnit 3.7.*, so
let's show it in the composer.json file. Also update
magento-composer-installer required version in order to make this
extension compatiable with other Magento extension installed via
composer.
Merge pull request #75 from vsushkov/vsushkov/fix-composer-json

Update composer.json
! Added events to test listener. Now possible to add observers to PHPUnit application initialization
Merge branch 'release/v0.3.1'
Merge tag 'vv0.3.1' into dev

Minor features release that introduces dispatching of events and updated composer.json file
! Initial version of mock proxy and helpers
! Added main helper factory
Merge branch 'feature/test-helpers' of github.com:IvanChepurnyi/EcomDev_PHPUnit into feature/test-helpers