Add a space

Author: tiif

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -268,6 +268,7 @@ pub enum AttributeKind {
         /// Span of the attribute.
         span: Span,
     },
+
     /// Represents `#[unstable_feature_bound]`.
     UnstableFeatureBound(ThinVec<(Symbol, Span)>),
     // tidy-alphabetical-end