Fix Debian versions

7 and 8 are the currently supported versions, not 6 and 7. Derp.

metadata.json

@@ -1,6 +1,6 @@
 {
   "name": "ardichoke-arpwatch",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "author": "ardichoke",
   "summary": "Install and manage arpwatch",
   "license": "Apache-2.0",
@@ -19,8 +19,8 @@
       {
           "operatingsystem": "Debian",
           "operatingsystemrelease": [
-              "6",
-              "7"
+              "7",
+              "8"
           ]
       }
   ],