Change the internet connectivity check from a ping to a wget.

1) The ping is not a true test of whether the proxy is configured correctly and able to "proxy" the fedy downloads.
2) If ICMP traffic is blocked (in my case), the Internet Connectivity warning still comes up when starting fedy but it can still connect to the internet for downloads.It's misleading and
may confuse the user.

wget is already a prerequisite for fedy so it does not introduce an additional dependency.