patch 8.0.1455: if $SHELL contains a space then 'shell' is incorrect

Problem:    If $SHELL contains a space then the default value of 'shell' is
            incorrect. (Matthew Horan)
Solution:   Escape spaces in $SHELL. (Christian Brabandt, closes #459)
diff --git a/src/version.c b/src/version.c
index 5704074..69ba3f5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1455,
+/**/
     1454,
 /**/
     1453,