Check wc_checkout_params.is_checkout against string '1' instead of int 1

This was causing `’init_checkout’` not to be triggered on page load. I
noticed this when the taxes for an order weren’t being shown on the
checkout page until changing the billing address.

Introduced in b85b1ab03bd5974bf2fa7ae01580faff49b2559e
updating coupon email restriction tool tip
Merge pull request #5249 from BFTrick/coupon-email-restriction

Clarifying The Coupon Email Restriction Tool Tip
Merge pull request #5248 from maxrice/master

Use is_ssl() for get_woocommerce_api_url()
Merge pull request #5236 from JDGrimes/master

Check wc_checkout_params.is_checkout against string '1' instead of int 1
Chunk option names in cleanup_sessions() Closes #5225
Ensure _order_currency is set. Closes #5232