fix console block fence

Author: jnavila

book/01-introduction/sections/help.asc

@@ -42,5 +42,6 @@ usage: git add [<options>] [--] <pathspec>...
     --refresh             don't add, only refresh the index
     --ignore-errors       just skip files which cannot be added because of errors
     --ignore-missing      check if - even missing - files are ignored in dry run
-    --chmod <(+/-)x>      override the executable bit of the listed files----
+    --chmod <(+/-)x>      override the executable bit of the listed files
+----