patch 8.1.0528: various typos in comments

Problem:    Various typos in comments.
Solution:   Fix the typos.
diff --git a/src/gui_xmebw.c b/src/gui_xmebw.c
index 9ea020f..b09b1e6 100644
--- a/src/gui_xmebw.c
+++ b/src/gui_xmebw.c
@@ -50,7 +50,7 @@
  * implementation.  Also missing in Motif 1.2 and earlier.
  *
  * We neither use XmeGetPixmapData or _XmGetPixmapData, since with LessTif the
- * pixmap will not appear in it's caches properly. We cache the interesting
+ * pixmap will not appear in its caches properly. We cache the interesting
  * values in XmEnhancedButtonPart instead ourself.
  */
 #if defined(LESSTIF_VERSION) || (XmVersion <= 1002)