Use git clone --depth-1 instead of --single-branch to clone starters

[devrelm]

Description

Re-implements #729/#730.

I'm having trouble figuring out where the change from #730 was removed, but it looks like it was originally added to packages/gatsby/lib/utils/init-starter.js in 35b971b/#899, then copied over to packages/gatsby-cli/src/init-starter.js d737cd3.

Using --depth=1 instead of --single-branch shaved a couple seconds off of gatsby new gatsby-starter-blog https://github.com/gatsbyjs/gatsby-starter-blog.

Related Issues

Related to #729/#730

[KyleAMathews]

Oh wild — not sure how that happened! Thanks for fixing this old mixup!

[gatsbot]

Holy buckets, @devrelm — we just merged your PR to Gatsby! 💪💜

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[KyleAMathews]

Published in 2.8.19 — cloning the default starter went from 2329 objects to 28! Much faster!