Fix file_system dependency

[maltoe]

Hi :wave:

We recently hit a dependency resolution failure where a package (lightning_css) depended on not-too-old file_system ~> 0.2.10 and hence conflicted with phoenix_live_reload's dependency. I've submitted a patch to this package as well to bump the dep to v1.0.0, but some more research led to the following interesting find:

• file_system used to be called ExFsWatch more than 7 years ago. This package had versions going up to v0.4.2
• After the rename to file_system, version numbering started again at v0.1.1 and went up to v0.2.10 until version was bumped to v1.0.0. Weirdly enough, this all happens in the same repository and there are tags for all versions.
• There never was a file_system v0.3.0 and the dependency in mix.exs is wrong. Looking at recent changes, it seems safe to still include v0.2.10.

[josevalim]

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