New release: card.io 5.3.0 for Android

[Jeff Brateman]

Hello from card.io!

We have posted version 5.3.0 of card.io for Android to GitHub (https://github.com/card-io/card.io-Android-SDK). 

From the release notes:

5.3.0
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* Add option for only numeric input for postal code, `EXTRA_RESTRICT_POSTAL_CODE_TO_NUMERIC_ONLY` [#100](https://github.com/card-io/card.io-Android-SDK/issues/100).

Thanks!
@cardio