Revert "Updating Travis-CI configuration."

This reverts commit 9c05ce530f51d6ea2b8254d275bdfba9730c43f2.

Mistakingly increased required PHP version.
Revert "Fixing required PHP version (5.3.9+)."

This reverts commit 6b3aae8cfeec4f0c69fbe941c3e48e019f10647d.

Mistakingly increased required PHP version.