Update postfx package version

ScriptableRenderPipeline/Core/package.json

     "version": "1.0.0-beta",
     "unity": "2018.1",
     "dependencies": {
-        "com.unity.postprocessing": "2.0.0-beta"
+        "com.unity.postprocessing": "2.0.2-preview"
     }
 }

ScriptableRenderPipeline/HDRenderPipeline/package.json

     "version": "1.0.0-beta",
     "unity": "2018.1",
     "dependencies": {
-        "com.unity.postprocessing": "2.0.0-beta",
+        "com.unity.postprocessing": "2.0.2-preview",
         "com.unity.render-pipelines.core": "1.0.0-beta"
     }
 }

ScriptableRenderPipeline/LightweightPipeline/package.json

     "description": "Lightweight Render Pipeline for Unity.",
     "dependencies": {
         "com.unity.shadergraph": "1.0.0-beta",
-        "com.unity.postprocessing": "2.0.0-beta",
+        "com.unity.postprocessing": "2.0.2-preview",
         "com.unity.render-pipelines.core": "1.0.0-beta"
     },
     "version": "1.0.0-beta",

ScriptableRenderPipeline/master-package.json

     "version": "1.0.0-beta",
     "unity": "2018.1",
     "dependencies": {
-        "com.unity.postprocessing": "2.0.0-beta"
+        "com.unity.postprocessing": "2.0.2-preview"
     },
     "subPackages": [
         "Core",

package.json

 	"unity": "2018.1",
 	"description": "Render pipelines using SRP",
 	"dependencies": {
-    	"com.unity.postprocessing": "0.1.2"
+    	"com.unity.postprocessing": "2.0.2-preview"
 	}
 }