Fixing windows issue, also added 'build/' to .eslintrc

[ajmchambers]

Had a go at getting it working on windows:

• added library cross-env to get the NODE_PATH=source's working on windows
• fixed a couple of path's in the webpack config's

Unrelated but noticed lint was trying to lint the 'build/' folder (when it existed) and failing (on both windows and mac) so added it to the .eslintignore

(I'm still learning github and this whole process in general so let me know if I'm doing anything wrong, cheers.)

[ericelliott]

Looks good. Thanks!

[nkbt]

Good one :+1:

[gacosta89]

nice