Add row direction support

[bardiarastin]

this PR is for #1070 😊
all tests passing ✔
this adds row direction support to masonry (right to left cells)

[wuweiweiwu]

@bardiarastin I'm thinking of instead of having a rowDirection prop, just have it as a opt-in boolean prop/.

For example:

<Masonry
  {...this.props}
  rtl
/>

[bardiarastin]

@wuweiweiwu thanks for feedback, I had the same idea but this is from discussion in #1070

[wuweiweiwu]

@bardiarastin I see. Looks good to me 👍

[bvaughn]

Hi 👋 Looks like this PR broke CI because it wasn't formatted with Prettier first (yarn prettier) 😄

I fixed it (1e1746a) and pushed. Just an FYI.

[bardiarastin]

thanks @bvaughn, I made another PR to add yarn prettier to contributing docs 😬

[wuweiweiwu]

Woops. my bad. Do you think it is worth setting up CI for PRs? cc @bvaughn

[bardiarastin]

there are good free services for open source projects, it would be cool if it does not need spending a lot of time 😃