[pom] Depend on ehcache directly as most usage would

The ehcache-core was made internal long ago.  Any usage that has been upgrading was likely on ehcache directly not the noted 'internal' version.

pom.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
- Copyright 2010-2018 the original author or authors.
+ Copyright 2010-2019 the original author or authors.
 
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
@@ -79,8 +79,8 @@
  | compile dependencies
  -->
  <dependency>
- <groupId>net.sf.ehcache.internal</groupId>
- <artifactId>ehcache-core</artifactId>
+ <groupId>net.sf.ehcache</groupId>
+ <artifactId>ehcache</artifactId>
  <version>2.10.6</version>
  <scope>compile</scope>
  </dependency>