Fix TCP/DNS examples in the manual (#429)

The DNS examples needs fixing because the CNAME reference changed and
the Google free DNS server filters some test entries. Thus, I've
replaced the Google DNS server with the OpenDNS one where necessary.

docs/manual.md

@@ -421,9 +421,10 @@ If you want to keep your tests in separate files, the best way to obtain a singl
 Validates if a remote `address:port` are accessible.
 
 ```yaml
-tcp://ip-address-or-domain-name:80:
-  reachable: true
-  timeout: 500
+addr:
+  tcp://ip-address-or-domain-name:80:
+    reachable: true
+    timeout: 500
 ```
 
 
@@ -483,11 +484,11 @@ To validate specific DNS address types, prepend the hostname with the type and a
 ```yaml
 dns:
   # Validate a CNAME record
-  CNAME:dnstest.github.io:
+  CNAME:c.dnstest.io:
     resolvable: true
-    server: 8.8.8.8
+    server: 208.67.222.222
     addrs:
-    - "github.map.fastly.net."
+    - "a.dnstest.io."
 
   # Validate a PTR record
   PTR:8.8.8.8:
@@ -499,7 +500,7 @@ dns:
   # Validate and SRV record
   SRV:_https._tcp.dnstest.io:
     resolvable: true
-    server: 8.8.8.8
+    server: 208.67.222.222
     addrs:
     - "0 5 443 a.dnstest.io."
     - "10 10 443 b.dnstest.io."