Merge pull request #9 from ojacobson/static.json-is-optional

Restore optional nature of static.json.

scripts/config/lib/ngx_mruby/headers.rb

@@ -3,7 +3,8 @@ eval(File.read('/app/bin/config/lib/nginx_config_util.rb'))
 
 USER_CONFIG = "/app/static.json"
 
-config = JSON.parse(File.read(USER_CONFIG))
+config = {}
+config = JSON.parse(File.read(USER_CONFIG)) if File.exist?(json_file)
 req    = Nginx::Request.new
 uri    = req.var.uri