Fix failing jest tests with constructor

[cranesandcaff]

This PR adds a constructor to the Icon react class. This allows Jest unit tests to pass. We had an issue where our unit tests would fail unless we patched this class.

[szholdiyarov]

hey @cranesandcaff

Thanks for your contribution 👍🏼

Could you please give a more detailed explanation of the issue you had with running your unit tests? Did you try to mock that file?

[cranesandcaff]

GeekyAnts/NativeBase#2657
#1046
https://stackoverflow.com/questions/55530292/cannot-read-property-default-of-undefined-while-testing-application-with-jest

We could mock the icon but this will fix it for many people and save a lot of mental energy around using the project with no downsides.

[cranesandcaff]

Any thoughts on this? Seems like a low or no risk & high reward merge..

[hoblin]

That's another way to fix these fails #1157