Update the release build yaml with the latest versions (#783)

Author: pwshBot

.vsts-ci/releasebuild.yml

@@ -4,9 +4,9 @@ parameters:
   - name: 'previewReleaseTag'
     default: 'v7.4.0-rc.1'
   - name: 'ltsReleaseTag'
-    default: 'v7.2.16'
+    default: 'v7.2.17'
   - name: 'stableReleaseTag'
-    default: 'v7.3.9'
+    default: 'v7.4.0'
 
 resources:
 - repo: self