Updated corneltek/curlkit to the latest version containing c9s/CurlKit#6

[morozov]

Under certain circumstances, the downloader may use HTTP/2, in which case the download will fail:

$ phpbrew install 7.1.31
===> phpbrew will now build 7.1.31
---> Parsing variants from command arguments '+curl +default +fpm +gd +gmp +iconv +intl +ldap +mysql +sqlite +soap'
===> Loading and resolving variants...
Downloading https://secure.php.net/get/php-7.1.31.tar.bz2/from/this/mirror via curl extension

Fatal error: Uncaught CurlKit\CurlException:  at [The Location header can not be found: HTTP/2 302 
server: myracloud
date: Sun, 11 Aug 2019 23:38:06 GMT
content-type: text/html; charset=utf-8
content-language: en
x-frame-options: SAMEORIGIN
set-cookie: COUNTRY=NA%2C82.199.157.54; expires=Sun, 18-Aug-2019 23:38:06 GMT; Max-Age=604800; path=/; domain=.php.net
x-php-load: 0.12, 0.13, 0.1
status: 302 Found
location: https://www.php.net/distributions/php-7.1.31.tar.bz2
expires: Sun, 11 Aug 2019 23:38:06 GMT
cache-control: max-age=0] in vendor/corneltek/curlkit/src/CurlKit/CurlDownloader.php on line 180

This is resolved in c9s/CurlKit#6, so bumping the locked version. The dependency version is locked to c9s/CurlKit@9e85064 since it's the last commit that doesn't contain the changes introduced by c9s/CurlKit#4.

Fixes #1011.
Fixes #1023.

[coveralls]

Coverage decreased (-0.3%) to 40.003% when pulling 53123ec on morozov:curlkit-update into a3745f8 on phpbrew:master.