fix: use pipeline trigger constraint for nightly builds

.drone.yml

@@ -44,6 +44,14 @@ platform:
 clone:
   disable: true
 
+trigger:
+  branch:
+  - master
+  event:
+  - cron
+  cron:
+  - nightly
+
 steps:
 - name: call webhook
   pull: always
@@ -55,13 +63,6 @@ steps:
     - apk add --no-cache curl
     - curl -sO https://git.dotya.ml/${DRONE_REPO}/raw/branch/master/curl.it
     - bash ./curl.it -n $ENDPOINT
-  when:
-    branch:
-    - master
-    event:
-    - cron
-    cron:
-      - nightly
 
 
 ---