Update pollster requirement from 0.2 to 0.3 (#142)

Updates the requirements on [pollster](https://github.com/zesterer/pollster) to permit the latest version.
- [Release notes](https://github.com/zesterer/pollster/releases)
- [Changelog](https://github.com/zesterer/pollster/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zesterer/pollster/commits)

---
updated-dependencies:
- dependency-name: pollster
  dependency-type: direct:production
...

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Cargo.toml

@@ -40,7 +40,7 @@ winapi = { version = "0.3", features = ["d3d12","d3d11"] }
 wio = "0.2"
 
 [dev-dependencies]
-pollster = "0.2"
+pollster = "0.3"
 wgpu = "0.15"
 wgpu-subscriber = "0.1.0"
 winit = "0.28"