[ANN] packetgen 3.1.8 released

packetgen 3.1.8 has been released.

* home: <GitHub - sdaubert/packetgen: Ruby library to easily generate and capture network packets>
* bugs: <Issues · sdaubert/packetgen · GitHub>
* doc: <Home · sdaubert/packetgen Wiki · GitHub>

PacketGen provides simple ways to generate, send and capture network
packets.

Supported protocols are: Ethernet, Dot11, Dot1x, ARP, IP, IPv6, GRE,
ICMP, IGMP, ICMPv6, MLD, MLDv2, OSPFv2, OSPFv3, UDP, TCP, SNMP, DNS,
EAP, BOOTP, DHCP, TFTP, HTTP and MDNS.

Changes:

### 3.1.8 / 2021-03-13

* Revert depedency on pcaprub from 0.13 to 0.12 to let PacketGen run on
Ruby 3.

### 3.1.7 / 2020-12-23

* Update minimal Ruby version to 2.4
* Fix some limitations on Types::String and Types::CString