Show webpack errors when compilation fails
Show webpack errors when compilation fails

Right now webpack compilation errors are swallowed and the compile task exits silently. This is causing a lot of confusion - is it yarn? is it Heroku? Is it me? See #116, #117, #90, etc.

This commit causes the errors to be displayed instead.
usertesting/webpacker,gauravtiwari/webpacker,shakacode/webpacker_lite,gauravtiwari/webpacker,usertesting/webpacker,rossta/webpacker,gauravtiwari/webpacker,rails/webpacker,Davidzhu001/webpacker,rossta/webpacker,usertesting/webpacker,rails/webpacker,rossta/webpacker,Davidzhu001/webpacker,Davidzhu001/webpacker,rossta/webpacker