remove cover path URL from README example because it throws a certificate error

[SuzanaK]

If I execute the curl command in the example, no book is created and this error is thrown:

GET /api/v1/books/j2dL3OOo7/download 404 25.539 ms - 72
server_1         | POST /api/v1/books 202 7.410 ms - 18
server_1         | error: Error Thrown @ BookServices.createCover: Error: certificate has expired
server_1         |  error=Error: certificate has expired
server_1         |     at TLSSocket.onConnectSecure (_tls_wrap.js:1502:34)
server_1         |     at TLSSocket.emit (events.js:314:20)
server_1         |     at TLSSocket._finishInit (_tls_wrap.js:937:8)
server_1         |     at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:711:12)
server_1         | error: downloading coverPath https://via.placeholder.com/600x800.jpg?text=A%20Cover failed message=certificate has expired, stack=Error: certificate has expired
server_1         |     at TLSSocket.onConnectSecure (_tls_wrap.js:1502:34)
server_1         |     at TLSSocket.emit (events.js:314:20)
server_1         |     at TLSSocket._finishInit (_tls_wrap.js:937:8)
server_1         |     at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:711:12), code=CERT_HAS_EXPIRED

I also get a certificate error if I try to open the URL in the browser. That's why I propose to remove the URL.

[haroldtreen]

Ah! Good catch - thanks for fixing this!

[wrobbins]

@SuzanaK does this still happen? https://via.placeholder.com/600x800.jpg?text=A%20Cover works without a cert error now.

This error wasn't a flaw with EPP rather placeholder.com let a certificate expire, which now seems to be corrected.