Make exception class package private.

Signed-off-by: Santiago Pericas-Geertsen <[email protected]>

config/config/src/main/java/io/helidon/config/MetaConfigException.java

@@ -19,7 +19,7 @@
 /**
  * Exception is thrown if problems are found while processing meta config.
  */
-public class MetaConfigException extends RuntimeException {
+class MetaConfigException extends RuntimeException {
 
     private static final long serialVersionUID = 1L;