Update KeyStore.getDefaultType​() specification to return pkcs12 as fallback

KeyStore.getDefaultType​() still refers to the jks format if the keystore.type security property isn't defined.

The default keystore type is PKCS12 since JDK 9. Perhaps the "jks" reference can be replaced with a "pkcs12" reference.

An alternative might be for the JDK to throw an Error if the keystore.type security property isn't defined ?