Change single quotes around private token to double quotes

doc/api/project_clusters.md

@@ -22,7 +22,7 @@ Parameters:
 Example request:
 
 ```shell
-curl --header 'Private-Token: <your_access_token>' "https://gitlab.example.com/api/v4/projects/26/clusters"
+curl --header "Private-Token: <your_access_token>" "https://gitlab.example.com/api/v4/projects/26/clusters"
 ```
 
 Example response:
@@ -192,7 +192,7 @@ Parameters:
 Example request:
 
 ```shell
-curl --header 'Private-Token: <your_access_token>' "https://gitlab.example.com/api/v4/projects/26/clusters/user" \
+curl --header "Private-Token: <your_access_token>" "https://gitlab.example.com/api/v4/projects/26/clusters/user" \
 -H "Accept: application/json" \
 -H "Content-Type:application/json" \
 -X POST --data '{"name":"cluster-5", "platform_kubernetes_attributes":{"api_url":"https://35.111.51.20","token":"12345","namespace":"cluster-5-namespace","ca_cert":"-----BEGIN CERTIFICATE-----\r\nhFiK1L61owwDQYJKoZIhvcNAQELBQAw\r\nLzEtMCsGA1UEAxMkZDA1YzQ1YjctNzdiMS00NDY0LThjNmEtMTQ0ZDJkZjM4ZDBj\r\nMB4XDTE4MTIyNzIwMDM1MVoXDTIzMTIyNjIxMDM1MVowLzEtMCsGA1UEAxMkZDA1\r\nYzQ1YjctNzdiMS00NDY0LThjNmEtMTQ0ZDJkZjM.......-----END CERTIFICATE-----"}}'
@@ -289,7 +289,7 @@ through the ["Add existing cluster to project"](#add-existing-cluster-to-project
 Example request:
 
 ```shell
-curl --header 'Private-Token: <your_access_token>' "https://gitlab.example.com/api/v4/projects/26/clusters/24" \
+curl --header "Private-Token: <your_access_token>" "https://gitlab.example.com/api/v4/projects/26/clusters/24" \
 -H "Content-Type:application/json" \
 -X PUT --data '{"name":"new-cluster-name","domain":"new-domain.com","api_url":"https://new-api-url.com"}'
 ```
@@ -383,5 +383,5 @@ Parameters:
 Example request:
 
 ```shell
-curl --request DELETE --header 'Private-Token: <your_access_token>' "https://gitlab.example.com/api/v4/projects/26/clusters/23"
+curl --request DELETE --header "Private-Token: <your_access_token>" "https://gitlab.example.com/api/v4/projects/26/clusters/23"
 ```