Changes for bevy 0.3.0

[programWhiz]

Not sure how to fix CI, the changes regarding "variable should not be mutable" are actually required mutable vars (but somehow the Rust checker doesn't see that). However, you can build/run examples and use this in your game.

[ncallaway]

I'll have a look at what's going on with the CI later today.

If I can't figure it out quickly, but everything is working locally for me, I'll disable the CI checks to get this merged in

[Dispersia]

You can see my changes for ci in this pull request: https://github.com/ncallaway/bevy_prototype_networking_laminar/pull/24/files#diff-b803fcb7f17ed9235f1e5cb1fcd2f5d3b2838429d4368ae4c57ce4436577f03f it's a pretty small change. It was a dependency in bevy itself.

This PR can be merged instead of mine as it basically does the same thing, just upgrades it to even the next step

[ncallaway]

@Dispersia Great, thanks. Sorry for the lack of action on your PR

[Dispersia]

no worries at all, i used it in my own project all the same haha

[programWhiz]

I hope your recommendation works @Dispersia , but the errors I'm seeing in the CI are actually "this reference shouldn't be mutable" warnings which are treated as errors (I fixed all true errors). However, the references do need to be mutable (learned that one the hard way). Something about the way the ResMut references are working in bevy 0.3.0 the compiler will somehow think things don't need to be mutable or something. One fix I didn't know how to do was to disable that warning.