Fix custom directive 'galleryitem' (pytorch#161)

Author: chsasank

custom_directives.py

@@ -88,7 +88,8 @@ def run(self):
             if 'intro' in self.options:
                 intro = self.options['intro'][:195] + '...'
             else:
-                intro = sphinx_gallery.gen_rst.extract_intro(abs_fname)
+                _, blocks = sphinx_gallery.gen_rst.split_code_and_text_blocks(abs_fname)
+                intro, _ = sphinx_gallery.gen_rst.extract_intro_and_title(abs_fname, blocks[0][1])
 
             thumbnail_rst = sphinx_gallery.backreferences._thumbnail_div(
                 dirname, basename, intro)