my attempt to fix #3735

an alternative to this would be to do something like
`\DeclareGraphicsExtensions{.pdf}` in the preamble

IPython/nbconvert/templates/latex/sphinx_base.tplx

@@ -359,7 +359,7 b' Note: For best display, use latex syntax highlighting. =))'
 ((*- endblock -*))
 
 ((*- block data_pdf -*))
-    ((( conditionally_center_output(insert_graphics(output.pdf_filename[:-4])) )))
+    ((( conditionally_center_output(insert_graphics(output.pdf_filename)) )))
 ((*- endblock -*))
 
 ((*- block data_latex *))