[gnome-calculator] Adapt to gtk+ binding changes with vala git/0.27

[Rico Tzschichholz <ricotz src gnome org>]

commit dbeea387e74b5fa258589c6143960cb72f2cf2b6
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Tue Nov 25 10:36:42 2014 +0100

    Adapt to gtk+ binding changes with vala git/0.27

 src/math-equation.vala |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/math-equation.vala b/src/math-equation.vala
index 8eade41..cb61057 100644
--- a/src/math-equation.vala
+++ b/src/math-equation.vala
@@ -241,7 +241,11 @@ public class MathEquation : Gtk.SourceBuffer
             @delete (ref ans_start, ref ans_end);
             get_iter_at_mark (out ans_start, ans_start_mark);
             get_iter_at_mark (out ans_end, ans_end_mark);
+#if VALA_0_28
+            insert_with_tags (ref ans_end, ans_text, -1, ans_tag);
+#else
             insert_with_tags (ans_end, ans_text, -1, ans_tag);
+#endif
 
             // NOTE: Due to the inverted gravity of answer marks, after inserting text
             //       the positions are inverted. Hence, we need to recreate marks.