gem: fix applicable rubocop todos

lib/dyndnsd/generator/bind.rb

@@ -14,21 +14,21 @@ module Dyndnsd
         out = []
         out << "$TTL #{@ttl}"
         out << "$ORIGIN #{@domain}."
-        out << ""
+        out << ''
         out << "@ IN SOA #{@dns} #{@email_addr} ( #{zone['serial']} 3h 5m 1w 1h )"
         out << "@ IN NS #{@dns}"
-        out << ""
-        zone['hosts'].each do |hostname,ips|
+        out << ''
+        zone['hosts'].each do |hostname, ips|
           ips.each do |ip|
             ip = IPAddr.new(ip).native
-            type = ip.ipv6? ? "AAAA" : "A"
+            type = ip.ipv6? ? 'AAAA' : 'A'
             name = hostname.chomp('.' + @domain)
             out << "#{name} IN #{type} #{ip}"
           end
         end
-        out << ""
+        out << ''
         out << @additional_zone_content
-        out << ""
+        out << ''
         out.join("\n")
       end
     end