api: add no cache headers for IE11

Adds pragma and expires headers for API calls so that IE11 does not
cache GET calls. Ref #5356

pkg/middleware/middleware.go

@@ -250,6 +250,8 @@ func AddDefaultResponseHeaders() macaron.Handler {
 	return func(ctx *Context) {
 		if ctx.IsApiRequest() && ctx.Req.Method == "GET" {
 			ctx.Resp.Header().Add("Cache-Control", "no-cache")
+			ctx.Resp.Header().Add("Pragma", "no-cache")
+			ctx.Resp.Header().Add("Expires", "-1")
 		}
 	}
 }