Resolve get_first clippy lint

    warning: accessing first element with `block.stmts.get(0)`
       --> src/expr.rs:915:20
        |
    915 |             match (block.stmts.get(0), block.stmts.get(1)) {
        |                    ^^^^^^^^^^^^^^^^^^ help: try: `block.stmts.first()`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#get_first
        = note: `-W clippy::get-first` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::get_first)]`

src/expr.rs

@@ -912,8 +912,8 @@ impl Printer {
         if attr::has_inner(attrs) || !block.stmts.is_empty() {
             self.space();
             self.inner_attrs(attrs);
-            match (block.stmts.get(0), block.stmts.get(1)) {
-                (Some(Stmt::Expr(expr, None)), None) if stmt::break_after(expr) => {
+            match block.stmts.as_slice() {
+                [Stmt::Expr(expr, None)] if stmt::break_after(expr) => {
                     self.ibox(0);
                     self.expr_beginning_of_line(expr, true);
                     self.end();