Add new age slot to bot

[UKnowWhoIm]

At the time of making this bot there were only 2 age slots

• 18-44(represented as 18)
• 45+(represented as 45)

CoWin has added a new age slot 40-44(represented as 40).

We've used this function in src/commands/common.js to set the age slot. Modify it to add the new age slot.

export const getAge = (age) => age >= 45 ? 45 : 18;