[unity] Editor asmdef.

spine-unity/Assets/Spine/Editor/spine-unity-editor.asmdef

@@ -4,7 +4,9 @@
         "spine-unity"
     ],
     "optionalUnityReferences": [],
-    "includePlatforms": [],
+    "includePlatforms": [
+        "Editor"
+    ],
     "excludePlatforms": [],
     "allowUnsafeCode": false
 }