Updates `license` key in `composer.json` to match `LICENSE` file.
Updates `license` key in `composer.json` to match `LICENSE` file.

Prior to this commit, `composer.json` specified `Apache 2.0` license whilst
the `LICENSE` file included the `MIT` license. This commit brings the two
back into sync.

Fixes issue #1.

dshafik/guzzlehttp-vcr