update 'functional' section reading list
update 'functional' section reading list

- add 'Mostly Adequate Guide To Functional Programming' to functional section recommended reading list
- fix typo: changed `soltion` to `solution`

https://github.com/dwyl/learn-tdd/issues/114

nelsonic/learn-tdd,dwyl/learn-tdd,dwyl/learn-tdd,nelsonic/learn-tdd