Update go dependencies

vendor/google.golang.org/appengine/appengine.go

@@ -60,6 +60,24 @@ func IsDevAppServer() bool {
 	return internal.IsDevAppServer()
 }
 
+// IsStandard reports whether the App Engine app is running in the standard
+// environment. This includes both the first generation runtimes (<= Go 1.9)
+// and the second generation runtimes (>= Go 1.11).
+func IsStandard() bool {
+	return internal.IsStandard()
+}
+
+// IsFlex reports whether the App Engine app is running in the flexible environment.
+func IsFlex() bool {
+	return internal.IsFlex()
+}
+
+// IsAppEngine reports whether the App Engine app is running on App Engine, in either
+// the standard or flexible environment.
+func IsAppEngine() bool {
+	return internal.IsAppEngine()
+}
+
 // NewContext returns a context for an in-flight HTTP request.
 // This function is cheap.
 func NewContext(req *http.Request) context.Context {