JavaScriptSDK Change return type to Promise (#831)

Author: jordan-playfab

targets/javascript/templates/PlayFab_Api.d.ts.ejs

@@ -9,7 +9,7 @@ declare module PlayFab<%- api.name %>Module {
 
 <% for(var cIdx in api.calls) { var apiCall = api.calls[cIdx];
 %><%- generateApiSummary("        ", apiCall, "summary", "https://docs.microsoft.com/rest/api/playfab/" + api.name.toLowerCase() + "/" + apiCall.subgroup.toLowerCase().replaceAll(" ","-") + "/" + apiCall.name.toLowerCase())
-%>        <%- apiCall.name %>(request: PlayFab<%- api.name %>Models.<%- apiCall.request %>, callback: PlayFabModule.ApiCallback<PlayFab<%- api.name %>Models.<%- apiCall.result %>>, customData?: any, extraHeaders?: { [key: string]: string }): void;
+%>        <%- apiCall.name %>(request: PlayFab<%- api.name %>Models.<%- apiCall.request %>, callback: PlayFabModule.ApiCallback<PlayFab<%- api.name %>Models.<%- apiCall.result %>>, customData?: any, extraHeaders?: { [key: string]: string }): Promise<PlayFabModule.ApiCallback<PlayFab<%- api.name %>Models.<%- apiCall.result %>>>;
 <% } %>
     }
 }