[balsa] Fixed typo

[Marek Černocký <mcernocky src gnome org>]

commit f3bba06ec3fdfa734f0aa15c2e7312ef5a8caf82
Author: Marek Cernocky <marek_cernocky conel cz>
Date:   Thu Aug 31 17:01:39 2017 +0200

    Fixed typo

 doc/C/win-filters.page |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/doc/C/win-filters.page b/doc/C/win-filters.page
index 847a499..c0fa8b7 100644
--- a/doc/C/win-filters.page
+++ b/doc/C/win-filters.page
@@ -192,7 +192,7 @@ id="win-filters">
           </item>
           <item>
             <p>
-            <gui>Date</gui> interval: you can input the interval by
+            <gui>Date interval</gui>: you can input the interval by
             the mean of the two text entries. A blank entry means
             no bound. The button tells to match when the message
             date is within the bounds or not. The sentence above