update mib doc

code says we want these 6 mibs. i trust the code.

lib/SNMP/Info/Layer3/Dell.pm

@@ -367,14 +367,18 @@ my $dell = new SNMP::Info::Layer3::Dell(...);
 
 =over
 
+=item F<DELL-REF-MIB>
+
 =item F<Dell-Vendor-MIB>
 
+=item F<RADLAN-COPY-MIB>
+
+=item F<RADLAN-HWENVIROMENT>
+
 =item F<RADLAN-Physicaldescription-MIB>
 
 =item F<RADLAN-rlInterfaces>
 
-=item F<RADLAN-HWENVIROMENT>
-
 =item Inherited Classes' MIBs
 
 See classes listed above for their required MIBs.