Bite 238. Write tests for Fibonacci

Note this is a Test Bite and uses Python 3.7 and MutPy 0.6.1

Our first Test Bite! The concept is simple: to pass a Test Bite, you write tests for the program under the "Code to Test" tab.

We run pytest-cov and MutPy against your code to see if your tests are strong enough (if interested, check out our full feature launch write-up).

To kick this off we have you write some tests for fib which generates a Fibonacci sequence. Good luck and let us know if you have any feedback.