Fix ics alert not working when a date is set

(cherry picked from commit fa847d9)

Author: giacomovernoni

.gitignore

@@ -1,3 +1,4 @@
+.idea
 build
 composer.lock
 docs

src/Generators/Ics.php

@@ -125,16 +125,16 @@ private function generateAlertComponent(Link $link): array
             $description = 'Reminder: '.$this->escapeString($link->title);
         }
 
-        $trigger = '-PT15M';
+        $trigger = 'TRIGGER:-PT15M';
         if (($reminderTime = $this->options['REMINDER']['TIME'] ?? null) instanceof \DateTimeInterface) {
-            $trigger = 'VALUE=DATE-TIME:'.gmdate($this->dateTimeFormat, $reminderTime->getTimestamp());
+            $trigger = 'TRIGGER;VALUE=DATE-TIME:'.gmdate($this->dateTimeFormat, $reminderTime->getTimestamp());
         }
 
         $alarmComponent = [];
         $alarmComponent[] = 'BEGIN:VALARM';
         $alarmComponent[] = 'ACTION:DISPLAY';
         $alarmComponent[] = 'DESCRIPTION:'.$description;
-        $alarmComponent[] = 'TRIGGER:'.$trigger;
+        $alarmComponent[] = $trigger;
         $alarmComponent[] = 'END:VALARM';
 
         return $alarmComponent;

tests/Generators/__snapshots__/IcsGeneratorTest__it_can_generate_with_a_custom_reminder__1.txt

@@ -12,7 +12,7 @@ LOCATION:Party Lane 1A\, 1337 Funtown
 BEGIN:VALARM
 ACTION:DISPLAY
 DESCRIPTION:Party with balloons and cake!
-TRIGGER:VALUE=DATE-TIME:20180201T081500Z
+TRIGGER;VALUE=DATE-TIME:20180201T081500Z
 END:VALARM
 END:VEVENT
 END:VCALENDAR