Update migration-pickers-v6.md

Fix small typo in dayOfWeekFormatter modified props code sample

Signed-off-by: Ryan Turinsky <Ryan.turinsky@gmail.com>

docs/data/migration/migration-pickers-v6/migration-pickers-v6.md

@@ -237,7 +237,7 @@ The string argument of the `dayOfWeekFormatter` prop has been replaced in favor
 
    // If you were already using the day object, just remove the first argument.
 -  dayOfWeekFormatter={(_dayStr, day) => `${day.format('dd')}.`
-+  dayOfWeekFormatter={day => `${day.format('dd')}.`
++  dayOfWeekFormatter={day => `${day.format('dd')}.`}
  />
 ```