Merge pull request 3b1b#1284 from niedong/typo-fix

fix typo docstring in scene_file_writer.py

manimlib/scene/scene_file_writer.py

@@ -427,7 +427,7 @@ def open_movie_pipe(self):
     def close_movie_pipe(self):
         """
         Used internally by Manim to gracefully stop writing to FFMPEG's
-        input buffer, and move the temporary files into their permananant
+        input buffer, and move the temporary files into their permanent
         locations
         """
         self.writing_process.stdin.close()