Describe the bug
Tried to set additional argument -d setting=STAGE=test, didn't appear in the curl command line.

Environment (please complete the following information):

• Operating system: Ubuntu 16.04
• Python version: 3.7.3
• ScrapydWeb version: 1.4.0
• Scrapyd version: 1.2.1
• Scrapyd amount 2
• Scrapy version: 2.2.1
• Browser Chrome 70