Refactors score component to define it as a function that take props.
As this makes for simpler and more understandable components (they also
prevent components from having state).
For testing this required installing enzyme a test library that
simplifies shallow render testing (built on: reacts inbuilt shallow
Note 1 - currently components as functions do not support shallow
compare that PureComponents do, unfortunately this negates one of the
many benefits of using immutable and persistent data structures.
Hopefully, this feature will be added in future.
Note 2 - components that are defined as functions that take props
do not currently support refs.
npm i --save-dev enzyme