It seems because of my git version.
When I used ubuntu 16.04, the git version is lower than I need, then I
installed new version manually.
After upgrade to 18.04, the new git version is higher than the former one and
it uses libcurl3, then the problem happened.
Now use the latest git version,
Same issue.
When I used git clone, it shows:
git-remote-https: /usr/lib/x86_64-linux-gnu/libcurl.so.4: version
`CURL_OPENSSL_3' not found (required by git-remote-https)
But when I installed libcurl3, it shows:
The following packages will be REMOVED:
libcurl4 virtualbox-5.2
>From the above
