Downgrade uglify-js to solve uglifyJS swap bug
Downgrade uglify-js to solve uglifyJS swap bug

test plan: it should be possible to build production assets
without consuming 50GB of memory

Change-Id: I54b885c831408d1bc1b3c57e2ded2fdf2442b609
Reviewed-on: https://gerrit.instructure.com/146365
Product-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Tested-by: Jenkins
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms