Updated SC2236 (markdown)

SC2236.md

@@ -20,6 +20,7 @@ if [ -n "$STY" ];       then echo "You are already running screen"; fi
 
 You have negated `test -z` or `test -n`, resulting in a needless double-negative. You can just use the other operator instead:
 
+```sh
 # Identical tests to verify that a value is assigned
 [ ! -z foo ] # Not has no value
 [ -n foo ]   # Has value
@@ -27,6 +28,7 @@ You have negated `test -z` or `test -n`, resulting in a needless double-negative
 # Identical tests to verify that a value is empty
 [ ! -n foo ] # Not is non-empty
 [ -z foo ]   # Is empty
+```
 
 ### Exceptions: