doc/filters: update hue command syntax after recent update

doc/filters.texi

@@ -6693,13 +6693,13 @@ Specify a list of drawtext and hue commands in a file.
          [leave] drawtext reinit 'fontfile=FreeSerif.ttf:text=';
 
 # desaturate the image in the interval 15-20
-15.0-20.0 [enter] hue reinit s=0,
+15.0-20.0 [enter] hue s 0,
           [enter] drawtext reinit 'fontfile=FreeSerif.ttf:text=nocolor',
-          [leave] hue reinit s=1,
+          [leave] hue s 1,
           [leave] drawtext reinit 'fontfile=FreeSerif.ttf:text=color';
 
 # apply an exponential saturation fade-out effect, starting from time 25
-25 [enter] hue s=exp(t-25)
+25 [enter] hue s exp(t-25)
 @end example
 
 A filtergraph allowing to read and process the above command list