add get method for isql

Author: iamazy

isql-plugin/src/main/java/io/github/iamazy/elasticsearch/dsl/plugin/RestSqlAction.java

@@ -51,9 +51,9 @@ public String getName() {
     public List<RestHandler.Route> routes() {
         List<RestHandler.Route> routes = new ArrayList<>(4);
         routes.add(new Route(RestRequest.Method.POST, "/_isql/_explain"));
-        routes.add(new Route(RestRequest.Method.POST, "/_isql/_explain"));
-        routes.add(new Route(RestRequest.Method.POST, "/_isql"));
+        routes.add(new Route(RestRequest.Method.GET, "/_isql/_explain"));
         routes.add(new Route(RestRequest.Method.POST, "/_isql"));
+        routes.add(new Route(RestRequest.Method.GET, "/_isql"));
         return routes;
     }