[gnome-calculator] Added Control+Delete shortcut to clear current equation (fixes #187)

[Robert Roth <robertroth src gnome org>]

commit 01edc824a05482dbde5dd89d59f0ca53f15fe511
Author: Robert Roth <robert roth off gmail com>
Date:   Mon Mar 8 11:24:58 2021 +0200

    Added Control+Delete shortcut to clear current equation (fixes #187)

 src/math-display.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/math-display.vala b/src/math-display.vala
index 8ecd7bdb..75d1f943 100644
--- a/src/math-display.vala
+++ b/src/math-display.vala
@@ -152,7 +152,7 @@ public class MathDisplay : Gtk.Viewport
         var state = event.state & (Gdk.ModifierType.CONTROL_MASK | Gdk.ModifierType.MOD1_MASK);
 
         if ((event.keyval == Gdk.Key.Escape && state == 0 && !completion_visible) ||
-            (event.keyval == Gdk.Key.Delete && state == Gdk.ModifierType.SHIFT_MASK))
+            (event.keyval == Gdk.Key.Delete && (event.state & Gdk.ModifierType.CONTROL_MASK) == 
Gdk.ModifierType.CONTROL_MASK))
         {
             equation.clear ();
             status_changed_cb ();