Update introduction.md

Co-authored-by: Anastasios Chatzialexiou <[email protected]>

Author: ErikSchierboom

exercises/swift-scheduling/introduction.md

@@ -2,5 +2,5 @@
 
 This week, it is your turn to take notes in the department's planning meeting.
 In this meeting, your boss will set delivery dates for all open work items.
-Annoyingly, instead of specifying the _actual_ delivery date, your boss will only _describe them_ in an annoying abbreviated format.
+Annoyingly, instead of specifying the _actual_ delivery dates, your boss will only _describe them_ in an abbreviated format.
 As many of your colleagues won't be familiar with this corporate lingo, you'll need to convert these delivery date descriptions to actual delivery dates.