Fix issue with importing type declarations from TS modules

[sraby]

When working on #2, I kept hitting this error. Ended up saving the custom type declarations in the src directory instead.

TS7016: Could not find a declaration file for module 'react-anchor-link-smooth-scroll'. '/home/runner/work/subway-quiz/subway-quiz/node_modules/react-anchor-link-smooth-scroll/lib/anchor-link.js' implicitly has an 'any' type.
  Try `npm i --save-dev @types/react-anchor-link-smooth-scroll` if it exists or add a new declaration (.d.ts) file containing `declare module 'react-anchor-link-smooth-scroll';`
     5 | import { Results } from "./components/Results";
     6 | import { getQuizContent } from "./data/quiz-content";
  >  7 | import AnchorLink from "react-anchor-link-smooth-scroll";

Maybe has to do with the duplication of the /subway-quiz directory in the pathname?