Fix constants typings (date-fns#2791)

Fixed constants not having proper TypeScript and Flow types.

src/constants/index.d.ts

@@ -1,2 +1,12 @@
+export const daysInWeek: number
 export const maxTime: number
+export const millisecondsInMinute: number
+export const millisecondsInHour: number
+export const millisecondsInSecond: number
 export const minTime: number
+export const minutesInHour: number
+export const monthsInQuarter: number
+export const monthsInYear: number
+export const quartersInYear: number
+export const secondsInHour: number
+export const secondsInMinute: number

src/constants/index.js.flow

@@ -1,4 +1,14 @@
 // @flow
 
+declare export var daysInWeek: number
 declare export var maxTime: number
+declare export var millisecondsInMinute: number
+declare export var millisecondsInHour: number
+declare export var millisecondsInSecond: number
 declare export var minTime: number
+declare export var minutesInHour: number
+declare export var monthsInQuarter: number
+declare export var monthsInYear: number
+declare export var quartersInYear: number
+declare export var secondsInHour: number
+declare export var secondsInMinute: number