You are working with a DataFrame named sales_df that contains various columns, including a column named 'Quantity', which is currently stored as a floating-point number. You know that the 'Quantity' column should represent whole numbers, and you want to convert it to an integer data type.
Write a line of code to convert the 'Quantity' column from a floating-point number to an integer within the DataFrame sales_df.
The answer should be in the following format:
sales_df['Quantity'] = #Your code here