The change-log is available online [1].
> ### Fixed in 7.55.1 - August 14 2017 ###
>
> Bugfixes:
>
> * build: fix 'make install' with configure, install docs/libcurl/* too
> * make install: add 8 missing man pages to the installation
> * curl: do bounds check using a double comparison
> * dist: Add dictserver.py/negtelnetserver.py to release
> * digest_sspi: Don't reuse context if the user/passwd has changed
> * gitignore: ignore top-level .vs folder
> * build: check out *.sln files with Windows line endings
> * travis: verify "make install"
> * dist: fix the cmake build by shipping cmake_uninstall.cmake.in too
> * metalink: fix error: ‘*’ in boolean context, suggest ‘&&’ instead
> * configure: use the threaded resolver backend by default if possible
> * mkhelp.pl: allow executing this script directly
> * maketgz: remove old *.dist files before making the tarball
> * openssl: remove CONST_ASN1_BIT_STRING
> * openssl: fix "error: this statement may fall through"
> * proxy: fix memory leak in case of invalid proxy server name
> * curl/system.h: support more architectures (OpenRISC, ARC)
> * docs: fix typos
> * curl/system.h: add Oracle Solaris Studio
> * CURLINFO_TOTAL_TIME: could wrongly return 4200 seconds
> * docs: --connect-to clarified
> * cmake: allow user to override CMAKE_DEBUG_POSTFIX
> * travis: test cmake build on tarball too
> * redirect: make it handle absolute redirects to IDN names
> * curl/system.h: fix for gcc on PowerPC
> * curl --interface: fixed for IPV6 unique local addresses
> * cmake: threads detection improvements
>
> ### Fixed in 7.55.0 - August 9 2017 ###
>
> Changes:
>
> * curl: allow --header and --proxy-header read from file
> * getinfo: provide sizes as curl_off_t
> * curl: prevent binary output spewed to terminal
> * curl: added --request-target
> * libcurl: added CURLOPT_REQUEST_TARGET
> * curl: added --socks5-{basic,gssapi}: control socks5 auth
> * libcurl: added CURLOPT_SOCKS5_AUTH
>
> […]
[1] https://curl.haxx.se/changes.html