Update node engine requirement

v0.21.1

Release v0.21.1

Various fixes, including translations

Includes fixes provided by the community:

• #395: New translation: Slovak;
• #403: Improved Japanese translation;
• #417: Improved Traditional Chinese translation;
• #492: Danish translation fixes;
• #498: Removal of npm as a direct dependency;
• #499: Upgrade of jQuery click events to the on syntax;
• #500: Fix for issues with time selection caused by DST.

Furthermore, yarn.lock was dropped and the minimum required node version bumped to ~4.9.1.

Fix out-of-bounds options when using `monthSelect` or `yearSelect`

This release includes the fix in #455, which provides a solution for the issues brought up in #412 and #452.

As a minor update, the files are now normalized to LF as the EOL character.

Add a `main` field to `package.json`

As discussed in #373, #438

Ukrainian language added

Thanks to @oslyak!

Refactor jQuery .bind() and .unbind() to .on() and .off()

This bumps the required jQuery version to >= 1.7

Thanks to @yonisolo

Prevent memory leak when unbinding document events

Includes #428 as provided by @monovertex, thanks!

Fix: Month UNDEFINED if shortcuts and monthSelect are enabled

Fixes #412

Thanks all!

Use moment to calculate the difference between dates

Fixes #310 using #423

Thanks to @jazanne for reporting, @calebcauthon for the confirmation and contribution and @wakirin and @yphoenix for the review! Great community effort.

Remove inline style

Thanks to @maximelafarie #393