Merge pull request #3943 from jdfreder/nbconvert_reveal_winfix

nbconvert: Serve post-processor Windows fix

IPython/nbconvert/post_processors/serve.py

@@ -41,6 +41,7 b' class ServePostProcessor(PostProcessorBase):'
 
         try:
             dirname, filename = os.path.split(input)
+            if dirname:
             os.chdir(dirname)
             httpd = HTTPServer(('127.0.0.1', 8000), SimpleHTTPRequestHandler)
             sa = httpd.socket.getsockname()