Add AppVeyor notifications to PSCore Slack #ci channel

appveyor.yml

@@ -2,6 +2,11 @@ environment:
   priv_key:
     secure: <encryped-value>
 
+notifications:
+  - provider: Slack
+    incoming_webhook:
+      secure: bwwXBTeJBtRFea6FSQKzVENLwL0AOeusUSUFIh/TeHA4y0UFk7bC9+OcxgZW+YfIC0VZyTpZClJHlPFFHSgiQs4g9om17RxzJEeq4EjsW5g=
+
 install:
   - ps: $fileContent = "-----BEGIN RSA PRIVATE KEY-----`n"
   - ps: $fileContent += $env:priv_key.Replace(' ', "`n")