[author] Update mathjs to 0.18.1
Merge pull request #2671 from josdejong/master

[author] Update mathjs to 0.18.1
[author] Update xlsx (npm auto-update)

Enable auto-update via npm
Updated packages via NPM auto-update.
seedrandom fix
seedrandom fix
Merge pull request #2678 from SheetJSDev/master

[author] Update xlsx (npm auto-update)