Add fail flag to pipeline trigger examples

If a pipeline fails to trigger, cURL still exist with
exit code zero. Example should use --fail to force
job to fail if pipeline didn't trigger.

Changelog: changed

app/views/projects/triggers/_index.html.haml

@@ -45,6 +45,7 @@
         %pre
           :plain
             curl -X POST \
+                 --fail \
                  -F token=TOKEN \
                  -F ref=REF_NAME \
                  #{builds_trigger_url(@project.id)}
@@ -54,7 +55,7 @@
         %pre
           :plain
             script:
-              - "curl -X POST -F token=TOKEN -F ref=REF_NAME #{builds_trigger_url(@project.id)}"
+              - "curl -X POST --fail -F token=TOKEN -F ref=REF_NAME #{builds_trigger_url(@project.id)}"
         %h5.gl-mt-3
           = _('Use webhook')
 
@@ -73,6 +74,7 @@
         %pre
           :plain
             curl -X POST \
+                 --fail \
                  -F token=TOKEN \
                  -F "ref=REF_NAME" \
                  -F "variables[RUN_NIGHTLY_BUILD]=true" \