Keep input out of error message and add test for slice Integer parsing.

lib/liquid/standardfilters.rb

@@ -323,7 +323,7 @@ module Liquid
       begin
         Integer(num)
       rescue ::ArgumentError
-        raise Liquid::ArgumentError, "invalid integer '#{num}'"
+        raise Liquid::ArgumentError, "invalid integer"
       end
     end
 

test/integration/standard_filter_test.rb

@@ -76,6 +76,7 @@ class StandardFiltersTest < Minitest::Test
     assert_equal '', @filters.slice(nil, 0)
     assert_equal '', @filters.slice('foobar', 100, 10)
     assert_equal '', @filters.slice('foobar', -100, 10)
+    assert_equal 'oob', @filters.slice('foobar', '1', '3')
     assert_raises(Liquid::ArgumentError) do
       @filters.slice('foobar', nil)
     end