Update sortedMerge.js

[annamatveev]

Shorter solution to the sortedMerge problem

[profnandaa]

Thanks for Anna your PR! 🎉

See my comment below.

In addition:

1. Fix the formatting, 2 spaces for tab will be good -- and be consistent. We'll add a linter later to help with this.
2. Instead of deleting the previous code, could your create a different file, e.g. sortedMerge-2.js

[profnandaa]

These slices might/will actually be expensive for large inputs; think about it.