Use Pimple\Container instead of Pimple for $configs

By using \Pimple instead of Container (already using Pimple\Container) it's throwing an exception:
Case mismatch between loaded and declared class names: Pimple vs Pimple\Container
Merge pull request #34 from andrewshell/patch-1

Use Pimple\Container instead of Pimple for $configs