Added missing `:` in gdscript example.

doc/classes/TileMap.xml

@@ -174,7 +174,7 @@
 				Overriding this method also overrides it internally, allowing custom logic to be implemented when tiles are placed/removed:
 				[codeblocks]
 				[gdscript]
-				func set_cell(x, y, tile, flip_x=false, flip_y=false, transpose=false, autotile_coord=Vector2())
+				func set_cell(x, y, tile, flip_x=false, flip_y=false, transpose=false, autotile_coord=Vector2()):
 				    # Write your custom logic here.
 				    # To call the default method:
 				    .set_cell(x, y, tile, flip_x, flip_y, transpose, autotile_coord)