Auto merge of #6304 - rust-lang:dependabot/cargo/env_logger-0.6.0, r=alexcrichton

Update env_logger requirement from 0.5.11 to 0.6.0

Updates the requirements on [env_logger](https://github.com/sebasmagri/env_logger) to permit the latest version.
<details>
<summary>Release notes</summary>

*Sourced from [env_logger's releases](https://github.com/sebasmagri/env_logger/releases).*

> ## 0.6.0
> # Key Changes
>
> - Set a policy for changes to the default format
> - Make all dependencies besides `log` optional (but enabled by default)
>
> # Breaking Changes
>
> - The default format is not considered stable across patch versions. The best way to get a stable format for later ripgrepping is to define a custom one.
> - All dependencies have been made optional except for `log`. That means compiling `env_logger` with `default-features=false` will result in a different experience than in `0.5.x`.
>
> # Contributions
>
> - [**hcpl**](https://github.com/hcpl) [Test with `-Z minimal-versions` on CI](https://github-redirect.dependabot.com/sebasmagri/env_logger/pull/114)
> - [**afck**](https://github.com/afck) [Add missing RFC3339 URL to fix rustdoc](https://github-redirect.dependabot.com/sebasmagri/env_logger/pull/105)
> - [Make all dependencies optional](https://github-redirect.dependabot.com/sebasmagri/env_logger/pull/100)
> - [Rework the default format](https://github-redirect.dependabot.com/sebasmagri/env_logger/pull/82)
> - [Don't clobber a previously set level filter](https://github-redirect.dependabot.com/sebasmagri/env_logger/pull/117)
>
> # More Details
>
> ## Disabling dependencies
>
> Using `default-features=false` will disable all dependencies of `env_logger` besides `log`. This will reduce compile times and alter the default format by disabling colours and timestamps.
>
> Disabling default dependencies is the recommended way to use `env_logger` for libraries that only need it for logging in tests.
</details>
<details>
<summary>Commits</summary>

- See full diff in [compare view](https://github.com/sebasmagri/env_logger/commits/v0.6.0)
</details>
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</details>

Cargo.toml

@@ -24,7 +24,7 @@ crossbeam-utils = "0.5"
 crypto-hash = "0.3.1"
 curl = { version = "0.4.19", features = ['http2'] }
 curl-sys = "0.4.15"
-env_logger = "0.5.11"
+env_logger = "0.6.0"
 failure = "0.1.2"
 filetime = "0.2"
 flate2 = "1.0.3"