Support for .swift and .dart files

[harshvats2000]

This extension doesn't work for .swift and .dart files.

[nirajkvinit]

Yes. Support added for both and more other relevant extensions. (https://github.com/nirajkvinit/LineSight/blob/fcb362b2a03562562fdcfc63677cd3402a9d3723/src/constants.ts)

Please review the PR.
#5