fix(breadcrumb): use flex-start for justify content

[alexander-riss]

ENG: this was probably a typo in the first place - autoprefixer flagged this when using spectrum-css, so fixing it here to get rid of the linter warning

To-do list

• If my change impacts other components, I have tested to make sure they don't break.
• If my change impacts documentation, I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• This pull request is ready to merge.

[lazd]

Note that start is a valid value for justify-content, it just doesn't respect flex-direction: row-reverse, whereas flex-start does. I tested the change locally and found it doesn't break RTL, so I think we're good to merge this.

That said, can you please paste the linter error that autoprefixer was showing you? Thanks!

[alexander-riss]

The warning was:
start value has mixed support, consider using flex-start instead

[alexander-riss]

any other objections? this warning is effectively blocking us from migrating to create-react-app 5.0 - as autoprefixer will log this warning during build time and in this way break any CI build

[lazd]

LGTM!