Fix rust analyzer error when translation file change

[wiiznokes]

fix https://github.com/kellpossible/cargo-i18n/issues/147

Tho, i'm not sure this is the best solution. I think a better one would be to use the build.rs file. cargo-i18n could provide an helper for this

[wiiznokes]

Using a build.rs in i18n-embed-fl would probably work, but there is the problem of retreiving the Manifest dir. We can't use the MANIFEST_DIR env variable, and using a custom env variable will probably not work when multiple crate are using i18n-embed-fl

[wiiznokes]

technicallty, we could use a custom env variable as a list of path. This might be the more elegant solution

[kellpossible]

@wiiznokes thanks for contribution! Currently a bit snowed under with other life things but I'll review as soon as I get the chance