don't quote atoms just for containing numerals

As long as the numeral is not the first character, it shouldn't force
quoting on the atom.  For example, abc123 does not need quotes.

src/lager_trunc_io.erl

@@ -297,6 +297,7 @@ atom_needs_quoting([]) ->
     false;
 atom_needs_quoting([H|T]) when (H >= $a andalso H =< $z);
                         (H >= $A andalso H =< $Z);
+                        (H >= $0 andalso H =< $9);
                          H == $@; H == $_ ->
     atom_needs_quoting(T);
 atom_needs_quoting(_) ->
@@ -400,6 +401,7 @@ atom_quoting_test() ->
     ?assertEqual("hello_world", lists:flatten(format("~p", ['hello_world'], 50))),
     ?assertEqual("'node@127.0.0.1'", lists:flatten(format("~p", ['node@127.0.0.1'], 50))),
     ?assertEqual("node@nohost", lists:flatten(format("~p", [node@nohost], 50))),
+    ?assertEqual("abc123", lists:flatten(format("~p", [abc123], 50))),
     ok.
 
 sane_float_printing_test() ->