[vala/0.42] libvaladoc: Properly support the output of async constructors

[Rico Tzschichholz <ricotz src gnome org>]

commit f3accdc68d021c6e289ee6e3873558be625b4387
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Thu Feb 14 17:35:04 2019 +0100

    libvaladoc: Properly support the output of async constructors
    
    Fixes https://gitlab.gnome.org/GNOME/vala/issues/753

 libvaladoc/api/method.vala | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/libvaladoc/api/method.vala b/libvaladoc/api/method.vala
index 9c12c8f16..de88d6ec6 100644
--- a/libvaladoc/api/method.vala
+++ b/libvaladoc/api/method.vala
@@ -193,10 +193,13 @@ public class Valadoc.Api.Method : Member, Callable {
                        if (is_inline) {
                                signature.append_keyword ("inline");
                        }
-                       if (is_yields) {
-                               signature.append_keyword ("async");
-                       }
+               }
 
+               if (is_yields) {
+                       signature.append_keyword ("async");
+               }
+
+               if (!is_constructor) {
                        signature.append_content (return_type.signature);
                }