Merge pull request #2555 from larsbrinkhoff/zone

Add .arpa to DNS Zone.

lib/linguist/languages.yml

@@ -754,6 +754,7 @@ DNS Zone:
   type: data
   extensions:
   - .zone
+  - .arpa
   tm_scope: text.zone_file
   ace_mode: text
 

samples/DNS Zone/sample.arpa

@@ -0,0 +1,13 @@
+$ORIGIN 0.0.0.c.2.1.0.3.0.0.2.1.e.f.f.3.ip6.arpa.
+$TTL     60
+@ 	 IN SOA ns root (
+	     2002042901 ; SERIAL
+	     7200       ; REFRESH
+	     600        ; RETRY
+	     36000000   ; EXPIRE
+	     120        ; MINIMUM
+	     )
+
+	    NS	 ns.example.com.
+
+c.a.7.e.d.7.e.f.f.f.0.2.8.0.a.0 PTR  sip01.example.com.