Bump phin, gatsby-plugin-sharp and gatsby-transformer-sharp

Removes [phin](https://github.com/ethanent/phin). It's no longer used after updating ancestor dependencies [phin](https://github.com/ethanent/phin), [gatsby-plugin-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sharp) and [gatsby-transformer-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-sharp). These dependencies need to be updated together.


Removes `phin`

Updates `gatsby-plugin-sharp` from 3.13.0 to 3.15.0
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-sharp/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-plugin-sharp)

Updates `gatsby-transformer-sharp` from 3.13.0 to 3.15.0
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-transformer-sharp/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-transformer-sharp)

---
updated-dependencies:
- dependency-name: phin
  dependency-type: indirect
- dependency-name: gatsby-plugin-sharp
  dependency-type: direct:production
- dependency-name: gatsby-transformer-sharp
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>