Update report output

docs/DeveloperGuide.md

@@ -928,7 +928,7 @@ Test case: `report r/low stock t/100`
 
 Expected: Prints Ham as it is the only item with quantity less than 100. Pie is not printed out as it has a quantity of exactly 100.
 ```
-There is 1 items low on stocks!
+There is 1 item low on stocks!
 1. Name: Ham
    Quantity: 0
 ```

src/main/java/supertracker/ui/Ui.java

@@ -129,7 +129,8 @@ private static String nothingSoldOpening(Item item) {
     private static String reportLowStockOpening(int quantity) {
         assert quantity >= 0;
         String isOrAre = quantity == 1 ? "is " : "are ";
-        return "There " + isOrAre + quantity + " items low on stocks!";
+        String plural = quantity == 1 ? EMPTY_STRING : "s";
+        return "There " + isOrAre + quantity + " item" + plural + " low on stocks!";
     }
 
     /**
@@ -594,7 +595,7 @@ public static void clearCommandSuccess(int transactionsCleared, LocalDate before
             printIndent("Nothing cleared. No transactions before " + dateString + " available to clear");
             return;
         }
-        String plural = transactionsCleared == 1 ? "" : "s";
+        String plural = transactionsCleared == 1 ? EMPTY_STRING : "s";
         printIndent(transactionsCleared + " transaction" + plural
                 + " before " + dateString + " successfully cleared!");
     }

src/test/java/supertracker/command/ReportCommandTest.java

@@ -67,7 +67,7 @@ public void reportCommand_lowStock_correctlyConstructed() throws TrackerExceptio
         Command c = Parser.parseCommand(userInput);
         c.execute();
 
-        String expected = "     There is 1 items low on stocks!" + LINE_SEPARATOR +
+        String expected = "     There is 1 item low on stocks!" + LINE_SEPARATOR +
                 "     1. Name: orange" + LINE_SEPARATOR +
                 "        Quantity: 10" + LINE_SEPARATOR;
         String actual = outContent.toString();