doc: use correct tls certificate property name

Docs referred to an `issuer` property being optionally present, when it
should have referred to the `issuerCertificate` property.

PR-URL: nodejs#10389
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/api/tls.md

@@ -583,13 +583,16 @@ For Example: `{ type: 'ECDH', name: 'prime256v1', size: 256 }`
 added: v0.11.4
 -->
 
-* `detailed` {boolean} Specify `true` to request that the full certificate
-  chain with the `issuer` property be returned; `false` to return only the
-  top certificate without the `issuer` property.
+* `detailed` {boolean} Include the full certificate chain if `true`, otherwise
+  include just the peer's certificate.
 
 Returns an object representing the peer's certificate. The returned object has
 some properties corresponding to the fields of the certificate.
 
+If the full certificate chain was requested, each certificate will include a
+`issuerCertificate` property containing an object representing its issuer's
+certificate.
+
 For example:
 
 ```text
@@ -600,24 +603,23 @@ For example:
      O: 'node.js',
      OU: 'Test TLS Certificate',
      CN: 'localhost' },
-  issuerInfo:
+  issuer:
    { C: 'UK',
      ST: 'Acknack Ltd',
      L: 'Rhys Jones',
      O: 'node.js',
      OU: 'Test TLS Certificate',
      CN: 'localhost' },
-  issuer:
-   { ... another certificate ... },
+  issuerCertificate:
+   { ... another certificate, possibly with a .issuerCertificate ... },
   raw: < RAW DER buffer >,
   valid_from: 'Nov 11 09:52:22 2009 GMT',
   valid_to: 'Nov  6 09:52:22 2029 GMT',
   fingerprint: '2A:7A:C2:DD:E5:F9:CC:53:72:35:99:7A:02:5A:71:38:52:EC:8A:DF',
   serialNumber: 'B9B0D332A1AA5635' }
 ```
 
-If the peer does not provide a certificate, `null` or an empty object will be
-returned.
+If the peer does not provide a certificate, an empty object will be returned.
 
 ### tlsSocket.getProtocol()
 <!-- YAML