Version-guard these specs

net-ftp 0.3.6+ returns the response from `put` and `puttextfile`.

See ruby/net-ftp#34

spec/ruby/library/net-ftp/shared/puttextfile.rb

@@ -34,8 +34,16 @@
     remote_lines.should == local_lines.gsub("\n", "\r\n")
   end
 
-  it "returns nil" do
-    @ftp.send(@method, @local_fixture_file, "text").should be_nil
+  guard -> { Net::FTP::VERSION < '0.3.6' } do
+    it "returns nil" do
+      @ftp.send(@method, @local_fixture_file, "text").should be_nil
+    end
+  end
+
+  guard -> { Net::FTP::VERSION >= '0.3.6' } do
+    it "returns the response" do
+      @ftp.send(@method, @local_fixture_file, "text").should == @ftp.last_response
+    end
   end
 
   describe "when passed a block" do