From "curl --manual", I found this:
curl -g "http://[2001:1890:1112:1::20]/"
So, for the address you're asking about, try:
curl -g "http://[::1]:8080/"
However, you may want to run:
and see if IPv6 shows up on the line that says "Features" (the third line, not counting extra lines from word wrapping). I found my version didn't. cURL download page has various links for operating systems, including curl 7.41.0 download site (which is currently the latest version) for Microsoft Windows. That page has multiple executables (available for Microsoft Windows); the first one I found did not support IPv6. But the two described as "ipv6-sspi-spnego-winssl" (one for x86 and one for x64) did : curl -V did show IPv6. So be careful about which package you download.