Fix output of Webpack errors
Fix output of Webpack errors

Seems like a webpack bug, but `stats.errors` seems to be missing some or
all of the time when there are in fact errors. Casting `stats.toJson()`
seems to do the trick.

outoftime/learnpad,jwang1919/popcode,jwang1919/popcode,popcodeorg/popcode,popcodeorg/popcode,popcodeorg/popcode,jwang1919/popcode,jwang1919/popcode,popcodeorg/popcode,outoftime/learnpad