Fix typescript typings

[mfedderly]

The typings for sweepline-intersections are slightly wrong, and causing issues in Turf.

https://arethetypeswrong.github.io/?p=sweepline-intersections%401.5.0

Rollup is actually using module.exports = sweeplineIntersections;, so this changes the types to match that.

You can examine what impact the various changes have by running npx @arethetypeswrong/cli and checking out the output, you may will have to build the package first.

In this case, I'm seeing this after making my change:

sweepline-intersections v1.5.0

Build tools:
- rollup@^2.7.6
- webpack@^4.29.0

 No problems found 🌟


┌───────────────────┬───────────────────────────┐
│                   │ "sweepline-intersections" │
├───────────────────┼───────────────────────────┤
│ node10            │ 🟢                        │
├───────────────────┼───────────────────────────┤
│ node16 (from CJS) │ 🟢 (CJS)                  │
├───────────────────┼───────────────────────────┤
│ node16 (from ESM) │ 🟢 (CJS)                  │
├───────────────────┼───────────────────────────┤
│ bundler           │ 🟢                        │
└───────────────────┴───────────────────────────┘

More information on the exact transformation I made here can be found in the DefinitelyTyped readme.