Update netty-all to 4.2.0.Final (#3890)

## About this PR
📦 Updates io.netty:netty-all from `4.1.119.Final` to `4.2.0.Final`

## Usage
✅ **Please merge!**

I'll automatically update this PR to resolve conflicts as long as you
don't change it yourself.

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have any feedback, just mention me in the comments below.

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[`.scala-steward.conf`](https://github.com/scala-steward-org/scala-steward/blob/8929fadb6f535472bd63397b1cb55a835fa1b5cb/docs/repo-specific-configuration.md)
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<details>
<summary>⚙ Adjust future updates</summary>

Add this to your `.scala-steward.conf` file to ignore future updates of
this dependency:
```
updates.ignore = [ { groupId = "io.netty", artifactId = "netty-all" } ]
```
Or, add this to slow down future updates of this dependency:
```
dependencyOverrides = [{
  pullRequests = { frequency = "30 days" },
  dependency = { groupId = "io.netty", artifactId = "netty-all" }
}]
```
</details>

<sup>
labels: library-update
</sup>

<!-- scala-steward = {
  "Update" : {
    "ForArtifactId" : {
      "crossDependency" : [
        {
          "groupId" : "io.netty",
          "artifactId" : {
            "name" : "netty-all",
            "maybeCrossName" : null
          },
          "version" : "4.1.119.Final",
          "sbtVersion" : null,
          "scalaVersion" : null,
          "configurations" : null
        }
      ],
      "newerVersions" : [
        "4.2.0.Final"
      ],
      "newerGroupId" : null,
      "newerArtifactId" : null
    }
  },
  "Labels" : [
    "library-update"
  ]
} -->

Author: xerial-bot

build.sbt

@@ -834,7 +834,7 @@ lazy val netty =
       name        := "airframe-http-netty",
       description := "Airframe HTTP Netty backend",
       libraryDependencies ++= Seq(
-        "io.netty" % "netty-all" % "4.1.119.Final"
+        "io.netty" % "netty-all" % "4.2.0.Final"
       )
     )
     .dependsOn(http.jvm, rx.jvm)
@@ -974,7 +974,7 @@ lazy val fluentd =
         "org.komamitsu" % "fluency-fluentd"      % FLUENCY_VERSION,
         "org.komamitsu" % "fluency-treasuredata" % FLUENCY_VERSION
         // td-client-java -> json-simple happened to include junit 4.10 [CVE-2020-15250]
-        exclude ("junit", "junit"),
+          exclude ("junit", "junit"),
         // Necessary for td-client-java, which is used in fluency-treasuredata
         "com.fasterxml.jackson.datatype" % "jackson-datatype-json-org" % "2.18.3" % Provided,
         "com.fasterxml.jackson.datatype" % "jackson-datatype-jdk8"     % "2.18.3" % Provided,