set http headers and bind fetch client

Author: tocsoft

Tocsoft.GraphQLCodeGen.Cli/Templates/ts/Function/typescript.template

@@ -3,7 +3,7 @@
 {{!# ClientClassDecorators }}
 
 {{!# FetchCient }}
-fetch
+window.fetch.bind(window)
 
 {{!# ApiUrl }}
 {{error 'TemplateSettings.ApiUrl or TemplateSettings.UrlConfig muse be specified for loading the api base url' }}
@@ -105,6 +105,7 @@ export class {{pascalCase Name}} {
 		export function {{camelCase OperationName}}({{> ArgumentList Arguments}}) : Promise<{{> TypeReference ResultType}}>{
         return client.fetch(url, {
             method : 'POST',
+            headers: {'Content-Type': 'application/json'},
             body : JSON.stringify({
                 query : `{{replace Query '`' '\`'}}`,
                 variables : {