patch 8.0.1038: strike-through text not supported

Problem:    Strike-through text not supported.
Solution:   Add support for the "strikethrough" attribute. (Christian
            Brabandt, Ken Takata)
diff --git a/src/terminal.c b/src/terminal.c
index faa74f7..05c0fd9 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -1735,7 +1735,7 @@
     if (cellattrs.italic)
 	attr |= HL_ITALIC;
     if (cellattrs.strike)
-	attr |= HL_STANDOUT;
+	attr |= HL_STRIKETHROUGH;
     if (cellattrs.reverse)
 	attr |= HL_INVERSE;
 
@@ -2451,7 +2451,7 @@
 	{"bold",      HL_BOLD},
 	{"italic",    HL_ITALIC},
 	{"underline", HL_UNDERLINE},
-	{"strike",    HL_STANDOUT},
+	{"strike",    HL_STRIKETHROUGH},
 	{"reverse",   HL_INVERSE},
     };