Merge pull request #60 from voxik/ruby24

Fix Ruby 2.4 compatibility.

Author: mfazekas

.travis.yml

@@ -5,6 +5,8 @@ rvm:
   - 2.1.0
   - 2.2.0
   - 2.3.0
+  - 2.4.0
+  - ruby-head
   - jruby-head
   - rbx-2
 

test/common.rb

@@ -70,7 +70,7 @@ def assert_progress_reported_put(offset, data, expect={})
 
     def assert_progress_reported_get(offset, data, expect={})
       assert_equal offset, current_event[3] if offset
-      if data.is_a?(Fixnum)
+      if data.is_a?(0.class)
         assert_equal data, current_event[4].length
       elsif data
         assert_equal data, current_event[4]