unity2018.1.9版导入了标准资源包Characters，导出PC平台时报错
unity2018.1.9版导入了标准资源包Characters，导出PC平台时报六个错误：
第一个
Assets/Standard Assets/CrossPlatformInput/Scripts/TouchPad.cs(49,13): error CS0012: The type UnityEngine.ISerializationCallbackReceiver' is defined in an assembly that is not referenced. Consider adding a reference to assemblyUnityEngine, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
第二个
Assets/Standard Assets/CrossPlatformInput/Scripts/TouchPad.cs(49,13): error CS0012: The type UnityEngine.ICanvasRaycastFilter' is defined in an assembly that is not referenced. Consider adding a reference to assemblyUnityEngine, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
第三个
Assets/Standard Assets/Utility/FPSCounter.cs(15,17): error CS0012: The type UnityEngine.MonoBehaviour' is defined in an assembly that is not referenced. Consider adding a reference to assemblyUnityEngine, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
第四个
Error building Player because scripts had compiler errors
第五个
Build completed with a result of 'Failed'
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
第六个
UnityEditor.BuildPlayerWindow+BuildMethodException: 4 errors
at UnityEditor.BuildPlayerWindow+DefaultBuildMethods.BuildPlayer (BuildPlayerOptions options) [0x0021f] in D:\unity\Editor\Mono\BuildPlayerWindowBuildMethods.cs:182
at UnityEditor.BuildPlayerWindow.CallBuildMethods (Boolean askForBuildLocation, BuildOptions defaultBuildOptions) [0x00065] in D:\unity\Editor\Mono\BuildPlayerWindowBuildMethods.cs:89
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
运行结果及报错内容
