I'm using

curl 7.52.1 (mipsel-openwrt-linux-gnu) libcurl/7.52.1 mbedTLS/2.5.1 Protocols: file ftp ftps http https Features: IPv6 Largefile SSL

from Onion's repo. Same problem :(

upd:
Fixed by

opkg install http://downloads.lede-project.org/snapshots/packages/mipsel_24kc/base/curl_7.54.1-1_mipsel_24kc.ipk opkg install http://downloads.lede-project.org/snapshots/packages/mipsel_24kc/base/libcurl_7.54.1-1_mipsel_24kc.ipk