Server version exposed

I am receiving Website Security Scan Report emails for all of my websites, stating:
New detected issues: Flagged by family filter, Flagged by security list
Flagged by family filter, Flagged by security list, Server version exposed
Security metric is  98%

How to address / resolve this on all of my sites?

Sample: Page info

• HTTP response code 202
• IP: 34.174.105.28
• Hostname IP: 28.105.174.34.bc.googleusercontent.com.
• Web server identified: nginx
• Security headers:
  • Content-Security-Policy: missing
  • Strict-Transport-Security: missing
  • X-Content-Type-Options: missing
  • X-Frame-Options: missing
• page size 166 bytes

The page I need help with: [log in to see the link]