[unity] Fixed timeline editor asmdef file for newer unity versions. See commit e4fefcf. See #1262.

spine-unity/Modules/com.esotericsoftware.spine.timeline/Editor/spine-timeline-editor.asmdef

@@ -2,7 +2,9 @@
     "name": "spine-timeline-editor",
     "references": [
         "spine-unity",
-        "spine-timeline"
+        "spine-unity-editor",
+        "spine-timeline",
+        "Unity.Timeline"
     ],
     "optionalUnityReferences": [],
     "includePlatforms": [],