Fix typo in link to Mutation.js
Fix typo in link to Mutation.js

### Context
```js
(path=".../hackernews-node/src/resolvers/Muation.js")
```

Muation.js is missspelled an should be Mutation.js

### Changes

-  Fixed typo
DevanB/howtographql,howtographql/howtographql,howtographql/howtographql,DevanB/howtographql,howtographql/howtographql