Updated to PHPUnit 4

Not working for these reasons:

__Tests:__
`Klein\Tests\KleinTest::testErrorsWithNoCallbacks`
`Klein\Tests\RoutingTest::testDispatchExceptionRethrowsUnknownCode`
`Klein\Tests\RoutingTest::testRoutePathCompilationFailure`
`Klein\Tests\RoutingTest::testRoutePathCompilationFailureWithoutWarnings`
`Klein\Tests\ServiceProviderTest::testRenderChunked`
`Klein\Tests\ServiceProviderTest::testValidate`
`Klein\Tests\ServiceProviderTest::testValidateParam`

__Error:__
```
Test code or tested code did not (only) close its own output buffers
```