Add bootstrap resolver with alternative port

[sergeevabc]

Dear @jedisct1,

My ISP does not allow me to connect to any resolvers on port 53, except for its own. So when DNSCrypt uses default bootstrap_resolvers = ['9.9.9.11:53', '8.8.8.8:53'] and I have no public-resolvers.md and public-resolvers.md.minisig files, there is a sad picture.

$ dnscrypt-proxy.exe

[NOTICE] dnscrypt-proxy 2.1.12
[NOTICE] Network connectivity detected
[NOTICE] Now listening to 127.0.0.1:53 [UDP]
[NOTICE] Now listening to 127.0.0.1:53 [TCP]
[NOTICE] Service is not usable yet
[NOTICE] Resolving server host [raw.githubusercontent.com] using bootstrap resolvers over udp
[NOTICE] Resolving server host [raw.githubusercontent.com] using bootstrap resolvers over tcp
[NOTICE] Bootstrap resolvers didn't respond - Trying with the system resolver as a last resort
[ERROR] Unable to resolve [raw.githubusercontent.com] - Make sure that the system resolver works, or that `bootstrap_resolvers` has been set to resolvers that can be reached
[NOTICE] Service is not usable yet
[NOTICE] Resolving server host [download.dnscrypt.info] using bootstrap resolvers over udp
[NOTICE] Resolving server host [download.dnscrypt.info] using bootstrap resolvers over tcp
[NOTICE] Bootstrap resolvers didn't respond - Trying with the system resolver as a last resort
[ERROR] Unable to resolve [download.dnscrypt.info] - Make sure that the system resolver works, or that `bootstrap_resolvers` has been set to resolvers that can be reached
[CRITICAL] Unable to retrieve source [public-resolvers]: [lookup download.dnscrypt.info: no such host]

The solution is simple, and I believe you should make it official for the common good.

Quad9 resolver supports an alternative port 9953 (faq, docs), so we change the configuration as follows

bootstrap_resolvers = ['9.9.9.10:9953', '8.8.8.8:53']

As a result, everything starts working as it should.

$ dnscrypt-proxy.exe

dnscrypt-proxy 2.1.12
Network connectivity detected
Now listening to 127.0.0.1:53 [UDP]
Now listening to 127.0.0.1:53 [TCP]
Service is not usable yet
Resolving server host [raw.githubusercontent.com] using bootstrap resolvers over udp
Source [relays] loaded
Source [public-resolvers] loaded
Firefox workaround initialized
Hot reload is disabled
...
Sorted latencies:
...
Server with the lowest initial latency: ... (rtt: 46ms)
dnscrypt-proxy is ready - live servers: 5