Fix test warnings when doing rake {test,spec} or script/test

test/test_document.rb

@@ -328,7 +328,7 @@ class TestDocument < JekyllUnitTest
     end
 
     should "be output in the correct place" do
-      assert_equal true, File.file?(@dest_file)
+      assert File.file?(@dest_file)
     end
   end
 

test/test_site.rb

@@ -465,7 +465,7 @@ class TestSite < JekyllUnitTest
       end
 
       should "print profile table" do
-        @site.liquid_renderer.should_receive(:stats_table)
+        expect(@site.liquid_renderer).to receive(:stats_table)
         @site.process
       end
     end