Fix Composer Setup

[hotwebmatter]

The latest Composer no longer matches the sha384sum hard-coded on line 11:

https://github.com/drupalpod/drupalpod-starterkit/blob/main/.gitpod/Dockerfile#L11

Luckily, there is a better way to install the latest Composer programmatically.

Patch incoming.

[hotwebmatter]

#19