Lint issues fixed.

templates/CONTRIBUTING.md.j2

@@ -29,7 +29,7 @@ In you own GitHub namespace, make the required changes.
 
 I typically do that by cloning the repository (in your namespace) locally:
 
-```
+```shell
 git clone git@github.com:YOURNAMESPACE/ansible-role-{{ role_name }}.git
 ```
 
@@ -39,19 +39,19 @@ Now you can start to edit on your laptop.
 
 Install [molecule](https://molecule.readthedocs.io/en/stable/) and [Tox](https://tox.readthedocs.io/):
 
-```
+```shell
 pip install molecule tox ansible-lint docker
 ```
 
 And run `molecule test`. If you want to test a specific distribution, set `image` and optionally `tag`:
 
-```
+```shell
 image=centos tag=7 molecule test
 ```
 
 Once it start to work, you can test multiple version of Ansible:
 
-```
+```shell
 image=centos tag=7 tox
 ```