Update rollup to v2.45.x

[fedetibaldo]

Fixes #83

My project build was failing, so I tracked down the issue to this module. It turned out that, as highlighted by other users, the rollup dependency was too low. I updated it and, as soon as I npm linked this new branch to my project, everything began to work smoothly again.

I've also shifted the range of supported node versions. I dropped the v4, v6, and v7 Travis jobs and added the v10, v12, and v14 jobs in their place. However, this shift has forced me to remove a total of 3 gulp plugins. Fortunately, none of them was essential to the ci task.

Because of the drastic dependency change, I've decided to mark this version as a major release. Please, let me know if a minor release would be better suited.

Final note: I committed the package-lock.json file. I believe this file to be important for future installs.

[fedetibaldo]

@kuraga, @mcasimir, are you interested in these changes?