Depending on the minification that's used having the `/*! ... comment ..*/` is helpful. I suggest adding the bang here so the custom builds do not have to modify the source that's generated and add a `!` to ensure they maintain the MIT copyright when minifying.
I think it's the custom build that reads from this file to add the license. I could be wrong, in which case, I hope the thing that does the custom build adds the `!` to the start of the copyright/license comment.