Error executing “ListObjects”

When I instal this plugin with php ver5.6.20 XAMPP, it show error message

Error executing “ListObjects” on “https://netbasejsc.sgp1.digitaloceanspaces.com/?prefix=test.txt%2F&max-keys=1&encoding-type=url”; AWS HTTP error: cURL error 60: SSL certificate problem: unable to get local issuer certificate (see http://curl.haxx.se/libcurl/c/libcurl-errors.html)

Please help me.

Thank you so much!