Build: Remove dates from copyright notice

I'm not too sure about the change in Gruntfile.js, so please let me know if you would like it to be different, e,g, whether the jquery.org/license should be on the same line as the Copyright notice, whether it should be https://jquery.org/ or https://jquery.org/license also, or anything else.
@mzgol Thanks for the comments. I'll make the changes now.