ISSUE_TEMPLATE: use "console" instead of non-existing "shell" syntax

```shell does not exist.
```sh is what you use to highligh (UNIX) shell scripts, and ```console
is what you use to highlight command lines.

.github/ISSUE_TEMPLATE.md

@@ -16,7 +16,7 @@ YOUR CODE
 ```
 
 Command Line
-```shell
+```console
 $ autopep8 
 ```