updated config example: PRIVATE_KEY is now ACCOUNT_KEY

docs/examples/config.sh.example

@@ -34,10 +34,10 @@
 #WELLKNOWN="${BASEDIR}/.acme-challenges"
 
 # Location of private account key (default: $BASEDIR/private_key.pem)
-#PRIVATE_KEY="${BASEDIR}/private_key.pem"
+#ACCOUNT_KEY="${BASEDIR}/private_key.pem"
 
 # Location of private account registration information (default: $BASEDIR/private_key.json)
-#PRIVATE_KEY_JSON="${BASEDIR}/private_key.json"
+#ACCOUNT_KEY_JSON="${BASEDIR}/private_key.json"
 
 # Default keysize for private keys (default: 4096)
 #KEYSIZE="4096"