Prepare release 3.8.1

CHANGELOG.md

 ## Changelog
 
+### 3.8.1
+  * Bugfix: Enable `attr_filter` module before service restart (thanks @theosotr)
+
 ### 3.8.0
   * Add proper support for perl modules (thanks @deligatedgeek)
 

metadata.json

 {
   "name": "jgazeley-freeradius",
-  "version": "3.8.0",
+  "version": "3.8.1",
   "author": "jgazeley",
   "summary": "Install and configure FreeRADIUS",
   "license": "Apache-2.0",