DateRangeInput placeholder not working

Environment

• Package version(s): @blueprintjs/datetime 3.18.5
• Operating System: macOS Big Sur Version 11.1
• Browser name and version: Chrome Version 87.0.4280.141 (Official Build) (x86_64)

Code Sandbox

Link to a minimal repro: https://codesandbox.io/s/blueprint-sandbox-forked-rk722?file=/src/DatetimeExample.tsx

Steps to reproduce

Specify placeholder on DateRangeInput e.g. "Please enter date"

Actual behavior

Placeholders say "Start date" and "End date"

Expected behavior

Placeholders should be the specified string e.g. "Please enter date"

Possible solution

Since there are two fields, the placeholder should be [string, string] for the start date and end date respectively