Bump major version to 3 for all packages

com.unity.render-pipelines.core/package.json

 {
     "name": "com.unity.render-pipelines.core",
     "description": "Core library for Unity render pipelines.",
-    "version": "2.0.0-preview",
+    "version": "3.0.0-preview",
     "unity": "2018.2",
     "displayName": "Render Pipeline Core Library",
     "dependencies": {

com.unity.render-pipelines.high-definition/package.json

 {
     "name": "com.unity.render-pipelines.high-definition",
     "description": "HD Render Pipeline for Unity.",
-    "version": "2.0.0-preview",
+    "version": "3.0.0-preview",
-        "com.unity.render-pipelines.core": "2.0.0-preview",
-        "com.unity.shadergraph": "2.0.0-preview"
+        "com.unity.render-pipelines.core": "3.0.0-preview",
+        "com.unity.shadergraph": "3.0.0-preview"
     }
 }

com.unity.render-pipelines.lightweight/package.json

 {
     "name": "com.unity.render-pipelines.lightweight",
     "description": "Lightweight Render Pipeline for Unity.",
-    "version": "2.0.0-preview",
+    "version": "3.0.0-preview",
-        "com.unity.render-pipelines.core": "2.0.0-preview",
-        "com.unity.shadergraph": "2.0.0-preview"
+        "com.unity.render-pipelines.core": "3.0.0-preview",
+        "com.unity.shadergraph": "3.0.0-preview"
     }
 }

com.unity.shadergraph/package.json

 {
     "name": "com.unity.shadergraph",
     "description": "Shader Graph",
-    "version": "2.0.0-preview",
+    "version": "3.0.0-preview",
     "unity": "2018.2",
     "displayName": "Shader Graph",
     "dependencies": {