Resolve "Documentation of `.gitlab-ci.yml` states incorrect example for variables"

doc/ci/variables/README.md

@@ -122,7 +122,7 @@ global defined variables in your job, define an empty array:
 ```yaml
 job_name:
-  variables: []
+  variables: {}
 ```
 You are able to use other variables inside your variable definition (or escape them with `$$`):

doc/ci/yaml/README.md

@@ -438,7 +438,7 @@ in your job, define an empty array:
 ```yaml
 job_name:
-  variables: []
+  variables: {}
 ```
 Job variables priority is defined in the [variables documentation][variables].