fix warnings in build.sbt

[xuwei-k]

Pull Request Checklist

• Have you read through the contributor guidelines?
• Have you signed the Typesafe CLA?
• Have you squashed your commits?
• Have you added copyright headers to new files?
• Have you checked that both Scala and Java APIs are updated?
• Have you updated the documentation for both Scala and Java sections?
• Have you added tests for any changed functionality?

Fixes

Fixes warnings

Purpose

Background Context

/home/travis/build/playframework/play-ws/build.sbt:122: warning: method copy in class AssemblyOption is deprecated (since 1.0.0): copy method is deprecated; use withIncludeBin(...) etc
  assembly / assemblyOption ~= (_.copy(includeScala = false)),
                                  ^
/home/travis/build/playframework/play-ws/build.sbt:125: warning: method copy in class AssemblyOption is deprecated (since 1.0.0): copy method is deprecated; use withIncludeBin(...) etc
    _.copy(includeScala = false)
      ^
/home/travis/build/playframework/play-ws/build.sbt:223: warning: method copy in class AssemblyOption is deprecated (since 1.0.0): copy method is deprecated; use withIncludeBin(...) etc
    assembly / assemblyOption := (assembly / assemblyOption).value.copy(includeBin = false, includeScala = false),
                                                                   ^
/home/travis/build/playframework/play-ws/build.sbt:248: warning: method copy in class AssemblyOption is deprecated (since 1.0.0): copy method is deprecated; use withIncludeBin(...) etc
    assembly / assemblyOption := (assembly / assemblyOption).value.copy(includeBin = false, includeScala = false),
                                                                   ^

References

sbt/sbt-assembly#433

[xuwei-k]

remove duplicate setting