Update bash.md

bash.md

@@ -1,4 +1,4 @@
----
+(---
 title: Bash scripting
 category: CLI
 layout: 2017/sheet
@@ -217,7 +217,7 @@ echo ${STR^^}  #=> "HELLO WORLD!" (all uppercase)
 | `${FOO:-val}`        | `$FOO`, or `val` if unset (or null) |
 | `${FOO:=val}`        | Set `$FOO` to `val` if unset (or null) |
 | `${FOO:+val}`        | `val` if `$FOO` is set (and not null) |
-| `${FOO:?message}`    | Show error message and exit if `$FOO` is unset (or is null) |
+| `${FOO:?message}`    | Show error message and exit if `$FOO` is unset (or null) |
 
 Omitting the `:` removes the (non)nullity checks, e.g. `${FOO-val}` expands to `val` if unset otherwise `$FOO`.