Unity.SerializedDictionary.Editor.asmdef targeting all platforms

[TheXRMonk]

editor scripts are being build to all targets

[Prastiwar]

Hello, since I don't use Unity anymore and can't find exact platform values to put in the json file, feel free to make pull request with changes to https://github.com/Prastiwar/UnitySerializedDictionary/blob/master/Editor/Unity.SerializedDictionary.Editor.asmdef and exclude them except the Editor ones