Add ltrim to lists

See https://redis.io/commands/ltrim/

Author: etiennebarrie

lib/kredis/types/list.rb

@@ -1,5 +1,5 @@
 class Kredis::Types::List < Kredis::Types::Proxying
-  proxying :lrange, :lrem, :lpush, :rpush, :exists?, :del
+  proxying :lrange, :lrem, :lpush, :ltrim, :rpush, :exists?, :del
 
   attr_accessor :typed
 

test/types/list_test.rb

@@ -57,4 +57,10 @@ class ListTest < ActiveSupport::TestCase
     @list.append(%w[ 1 2 3 ])
     assert @list.exists?
   end
+
+  test "ltrim" do
+    @list.append(%w[ 1 2 3 4 ])
+    @list.ltrim(-3, -2)
+    assert_equal %w[ 2 3 ], @list.elements
+  end
 end