appveyor.yml: send AppVeyor slack notification

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62360 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

appveyor.yml

@@ -53,3 +53,9 @@ test_script:
   - nmake -l test-spec
 matrix:
   fast_finish: true
+notifications:
+  - provider: Slack
+    incoming_webhook:
+      secure: WHfGy/gGheFHswUm9HsjNj3zDfbFX7UIGentpC1Z8eHeExOoJKoUSDYLxcw+15GYRnhZWL1LCtNdguTQ23bJRrS9tWeJ66OQ/msj5bb0iz4= # #alerts
+    on_build_success: true # to test notification
+    on_build_failure: true