Update SDK (#8115)

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "3.0.100-preview-010184"
+    "version": "3.0.100-preview4-010309"
   },
   "msbuild-sdks": {
     "Yarn.MSBuild": "1.13.0"

korebuild-lock.txt

@@ -1,2 +1,2 @@
-version:3.0.0-build-20190219.1
-commithash:7effe75f1408a86a9c32b592192fea1097bdd3a3
+version:3.0.0-build-20190226.1
+commithash:6f01223531df91913e253760e93ccc595a418a36