Add dependency to imgui

Author: kroatoa

com.unity.postprocessing/package.json

@@ -5,7 +5,8 @@
     "unity": "2019.4",
     "unityRelease": "19f1",
     "description": "The post-processing stack (v2) comes with a collection of effects and image filters you can apply to your cameras to improve the visuals of your games.",
-    "dependencies": {
-      "com.unity.modules.physics": "1.0.0"
-    }
+  "dependencies": {
+    "com.unity.modules.physics": "1.0.0",
+    "com.unity.modules.imgui": "1.0.0"
+  }
 }