Make sure default output dir is set (goadesign#1750)

when using goagen programmatically.

Author: raphael

goagen/gen_main/generator.go

@@ -22,7 +22,7 @@ import (
 
 //NewGenerator returns an initialized instance of a JavaScript Client Generator
 func NewGenerator(options ...Option) *Generator {
-	g := &Generator{}
+	g := &Generator{OutDir: "."}
 
 	for _, option := range options {
 		option(g)