[Feature request] Use javascript mode for .mjs & .cjs files

[pufferfish101007]

.mjs (module js) & .cjs (commonjs i.e. using require) files are becoming more common, especially in the nodejs ecosystem. Ipbe found myself editing mjs files and having to set language highlighting to javascript manually, which is annoying. It would be great if these could be added as file extension for javascript. I've already made the necessary changes in https://github.com/pufferfish101007/acode/tree/patch-1, but didn't want to make a pr in case it got denied.