I've looked at the example code and saw some consistent issues related to code style. The changes applied to this PR fixes the following points:

- Differences of line breaks styles between multiple files
- Differences of if statements styles
- Unnecessary comment
- A typo on a JSDocs

---

There were line breaks between statements on `pages/index.js`
````
export async function getServerSideProps(context) {
  const { client } = await connectToDatabase()

  const isConnected = await client.isConnected() 

  return {
    props: { isConnected },
  }
}
```` 

And this wasn't being applied to the MongoDB utility:

````
export async function connectToDatabase() {
  if (cached.conn) return cached.conn
  if (!cached.promise) {
    const conn = {}
    const opts = {
      useNewUrlParser: true,
      useUnifiedTopology: true,
    }
{...}
````

And also, as shown in the snippet above, there are different styles of if statements being used. 

With that being said, the reason I made this PR is because I think that this kind of inconsistent arises questions when a contributor looks to the codebase, even if this is a simple example.