[Issue 18649] curl on Ubuntu 18.04 depends on libcurl4, .deb installer depends on libcurl3

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18649

--- Comment #2 from Seb <greensunny12 at gmail.com> ---
Background info on the rename:

https://launchpad.net/ubuntu/+source/curl/7.58.0-2ubuntu2

 Rename libcurl3 to libcurl4, because libcurl exposes an SSL_CTX via
    CURLOPT_SSL_CTX_FUNCTION, and this object changes incompatibly between
    openssl 1.0 and openssl 1.1.

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