fix: change HTTP method of endpoints from POST to GET

[hgsgtk]

The commit changes HTTP methods from POST to GET.

As we can see in the Chrome DevTools Protocol document. the endpoints are defined as follow.

• GET /json/version
• GET /json or /json/list
• GET /json/new?{url}
• GET /json/activate/{targetId}
• GET /json/close/{targetId}

https://chromedevtools.github.io/devtools-protocol/

Actually, there is no problem using the HTTP method POST, but it's better to use GET to comply with the API specification.