explicit default justifyContent value
explicit default justifyContent value

Summary:
make default justifyContent value explicit like alignItems

https://developer.mozilla.org/en-US/docs/Web/CSS/justify-content

https://developer.mozilla.org/en-US/docs/Web/CSS/align-items

https://developer.mozilla.org/en-US/docs/Web/CSS/align-content
Closes https://github.com/facebook/yoga/pull/293

Differential Revision: D4351597

Pulled By: emilsjolander

fbshipit-source-id: b65ff2284ede4d75f1cc5e22d4106042ab0b0d02

rmarinho/yoga,facebook/yoga,yihuang/css-layout,yihuang/css-layout,yihuang/css-layout,facebook/css-layout,rmarinho/yoga,facebook/yoga,facebook/css-layout,facebook/yoga,facebook/yoga,facebook/css-layout,rmarinho/yoga,rmarinho/yoga,rmarinho/yoga,rmarinho/yoga,yihuang/css-layout,rmarinho/yoga,yihuang/css-layout,facebook/yoga,yihuang/css-layout,yihuang/css-layout,rmarinho/yoga,rmarinho/yoga,facebook/yoga,facebook/css-layout,facebook/css-layout,rmarinho/yoga,facebook/yoga,facebook/css-layout,facebook/css-layout,yihuang/css-layout,facebook/yoga,yihuang/css-layout,facebook/yoga,facebook/css-layout,facebook/css-layout,facebook/yoga,yihuang/css-layout