fixing trailing whitespaces

doc/tutorials/video/background_subtraction/background_subtraction.rst

@@ -327,7 +327,7 @@ We discuss the main parts of the above code:
       //update the path of the current frame
       fn.assign(nextFrameFilename);
 
-   * Note that this example works only on image sequences in which the filename format is <n>.png, where n is the frame number (e.g., 7.png).
+   Note that this example works only on image sequences in which the filename format is <n>.png, where n is the frame number (e.g., 7.png).
 
 Results
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