Fix to use ansible-lint instead of ansible-lint.sh (#7047)

tests/scripts/ansible-lint.sh was written on the doc, but there was
not such file actually. We can use ansible-lint command to check
ansible yml files without any options.
This updates to use the command.

CONTRIBUTING.md

@@ -10,7 +10,7 @@ To install development dependencies you can use `pip install -r tests/requiremen
 
 #### Linting
 
-Kubespray uses `yamllint` and `ansible-lint`. To run them locally use `yamllint .` and `./tests/scripts/ansible-lint.sh`
+Kubespray uses `yamllint` and `ansible-lint`. To run them locally use `yamllint .` and `ansible-lint`
 
 #### Molecule