message: Fix missing "is" in tour
diff: @@ -282,8 +282,8 @@ impl<'a> Step {
  fn welcome() -> Column<'a, StepMessage> {
  Self::container("Welcome!")
  .push(Text::new(
  - "This a simple tour meant to showcase a bunch of widgets that \
  - can be easily implemented on top of Iced.",
  + "This is a simple tour meant to showcase a bunch of widgets \
  + that can be easily implemented on top of Iced.",
  ))
  .push(Text::new(
  "Iced is a renderer-agnostic GUI library for Rust focused on \
  