fix warnings in build.sbt
fix warnings in build.sbt

```
/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),
                                                                   ^
```
playframework/play-ws