Missing JS code samples in Use Checks tutorials

[amarantha-k]

Code samples for JS requests (ripple-lib1.x) under Use Checks tutorials are not displayed even though the code snippets are available in the repository. For example https://xrpl.org/cash-a-check-for-a-flexible-amount.html#example-checkcash-preparation-for-a-flexible-amount.

Since ripple-lib1.x is an older version, it would be better to update these samples to use the latest JS library.

[mDuo13]

Looks like another side effect of #1098.