Warnings don't use ember-cli's ui

[simonihmig]

The warning here (

fast-sourcemap-concat/lib/source-map.js

Line 220 in 3980bc2

this._warn('Warning: ignoring input sourcemap for ' + filename + ' because ' + err.message);

) breaks my xunit test report (invalid XML), when used as ember t --silent -r xunit. This is because it uses console.log directly instead of ember-cli's ui.writeLine, thus ignoring the --silent flag.