remove option!() from async keywords
diff --git a/src/expr.rs b/src/expr.rs
index a751bc3..7cede99 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -2136,7 +2136,7 @@
     named!(expr_unstable_async_closure(allow_struct: bool) -> Expr, do_parse!(
         begin: call!(grab_cursor) >>
         _attrs: many0!(Attribute::parse_outer) >>
-        _asyncness: option!(keyword!(async)) >>
+        _asyncness: keyword!(async) >>
         _movability: option!(keyword!(static)) >>
         _capture: option!(keyword!(move)) >>
         _or1: punct!(|) >>
@@ -2170,7 +2170,7 @@
     named!(unstable_async_block -> ExprVerbatim, do_parse!(
         begin: call!(grab_cursor) >>
         _attrs: many0!(Attribute::parse_outer) >>
-        _asyncness: option!(keyword!(async)) >>
+        _asyncness: keyword!(async) >>
         _movability: option!(keyword!(static)) >>
         _capture: option!(keyword!(move)) >>
         _body: syn!(Block) >>
diff --git a/src/item.rs b/src/item.rs
index cd4975f..feab364 100644
--- a/src/item.rs
+++ b/src/item.rs
@@ -998,7 +998,7 @@
         _vis: syn!(Visibility) >>
         _constness: option!(keyword!(const)) >>
         _unsafety: option!(keyword!(unsafe)) >>
-        _asyncness: option!(keyword!(async)) >>
+        _asyncness: keyword!(async) >>
         _abi: option!(syn!(Abi)) >>
         _fn_: keyword!(fn) >>
         _ident: syn!(Ident) >>
@@ -1546,7 +1546,7 @@
         _defaultness: option!(keyword!(default)) >>
         _constness: option!(keyword!(const)) >>
         _unsafety: option!(keyword!(unsafe)) >>
-        _asyncness: option!(keyword!(async)) >>
+        _asyncness: keyword!(async) >>
         _abi: option!(syn!(Abi)) >>
         _fn_: keyword!(fn) >>
         _ident: syn!(Ident) >>