Fix the documentation for Building Zabbix agent 2 on Windows

There are two typos on  the zabbix Building Zabbix agent 2 on Windows

documentation page.

First

@echo off
set PATH=%PATH%;c:\bin\mingw\bin
cmd

Should be

@echo off
set PATH=%PATH%;c:\mingw\bin
cmd

Second

Link

https://bintray.com/vszakats/generic/openssl/1.1.1d

is dead, we have to change it for a correct one