fix(logging) encode try-list as json and no longer use new-line

New-line characters in the logging are impossible to parse
correctly so should be prevented.

fixes #52

src/resty/dns/client.lua

@@ -318,7 +318,8 @@ local try_list_mt = {
       end
       l[i]="\n"
     end
-    return table_concat(l)
+    -- concatenate result and encode as json array
+    return '[ "' .. table_concat(l):gsub('"',"'"):gsub("\n",'", "') .. '" ]'
   end
 }