[folks] inspect: Adapt to binding change of Signal.add_emission_hook() in vala 0.41

[Rico Tzschichholz <ricotz src gnome org>]

commit 6a5c9e7e8daf4e1361709a75719c17c8c28a6c4b
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Fri Mar 23 17:55:11 2018 +0100

    inspect: Adapt to binding change of Signal.add_emission_hook() in vala 0.41
    
    https://git.gnome.org/browse/vala/commit/?id=1d4db9f276c2593f072313864c743c6dd16acf35
    
    Reviewed-by: Philip Withnall <withnall endlessm com>

 tools/inspect/signal-manager.vala |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/tools/inspect/signal-manager.vala b/tools/inspect/signal-manager.vala
index 4d1b648..7c5b17a 100644
--- a/tools/inspect/signal-manager.vala
+++ b/tools/inspect/signal-manager.vala
@@ -430,7 +430,11 @@ public class Folks.Inspect.SignalManager : Object
         return false;
 
       ulong hook_id = Signal.add_emission_hook (signal_id,
+#if VALA_0_42
+          detail_quark, this.emission_hook_cb);
+#else
           detail_quark, this.emission_hook_cb, null);
+#endif
 
       /* Store the hook ID so we can list or remove it later */
       HashMap<uint, ulong> hook_ids =