remove the preview flag as it is more stable that 1.x

Author: sandorfr

Tasks/Yarn/task.json

@@ -6,7 +6,6 @@
     "helpMarkDown": "[More Information](https://github.com/geeklearningio/gl-vsts-tasks-yarn/wiki/Yarn) (Version #{Version}#).\n\nDear Angular and Ember CLI users, please check our [known issues](https://github.com/geeklearningio/gl-vsts-tasks-yarn/wiki/Known-Issues)",
     "category": "Utility",
     "author": "Geek Learning",
-    "preview": "true",
     "visibility": [
         "Build",
         "Release"

Tasks/YarnInstaller/task.json

@@ -9,7 +9,6 @@
         "Build",
         "Release"
     ],
-    "preview": "true",
     "author": "Geek Learning",
     "version": {
         "Major": 0,