Polymer build not uglifying lazyload

[Miguel Angelo Mello]

Hi there,

When running polymer build, lint complain of lazyload-image.html script section.

Cheers,

$ polymer build --verbose
info:    Building application...
info:    Generating build/unbundled...
info:    Generating build/bundled...
warn:    Unable to uglify file /home/miguel/github/diretonamao/portal/www/bower_components/lazyload-image/lazyload-image.html_script_0.js
debug:
{ message: 'Unexpected token name «change», expected punc «;»',
  filename: 0,
  line: 18,
  col: 13,
  pos: 564}

[Shogo Sensui]

lazyload-image uses ES2015 syntax, so if build system does not support ES2015, error will occur.