Rollup merge of #24436 - fhahn:fix-small-typo, r=steveklabnik

Author: Manishearth

src/libsyntax/feature_gate.rs

@@ -399,7 +399,7 @@ impl<'a> Context<'a> {
         } else {
             self.gate_feature("custom_attribute", attr.span,
                        &format!("The attribute `{}` is currently \
-                                unknown to the the compiler and \
+                                unknown to the compiler and \
                                 may have meaning \
                                 added to it in the future",
                                 name));