Update README.md

version 2.8.1 (mitre#1918)

Merge pull request mitre#1851 from mitre/update28

update to 2.8

inline plugins (mitre#1684)

Upgrading VERSION to 2.6.65. Release notes to follow.

Upgrading VERSION to 2.6.64. Release notes to follow.

inline (mitre#1423)

adding training as a default plugin (mitre#1409)

inline plugins (mitre#1371)

adding streaming messages to footer (mitre#1310)