Upgrade the default Java Version to 8

With the release of Java 8u20 it is time to move to Java 8. This commit changes
the default Java version that will be used by the Buildpack to '1.8.0_+'.

[#70715740]

Author: Christopher Frost

config/open_jdk_jre.yml

@@ -14,16 +14,16 @@
 # limitations under the License.
 
 # Configuration for JRE repositories keyed by vendor
-# From Java 1.8 onwards, metaspace should be used instead of permgen.  Please see the documentation for more detail.
+# To go back to Java 7, permgen should be used instead of metaspace.  Please see the documentation for more detail.
 ---
 repository_root: "{default.repository.root}/openjdk/{platform}/{architecture}"
-version: 1.7.0_+
+version: 1.8.0_+
 memory_sizes:
-  # metaspace: 64m..
-  permgen: 64m..
+  metaspace: 64m..
+  # permgen: 64m..
 memory_heuristics:
   heap: 75
-  # metaspace: 10
-  permgen: 10
+  metaspace: 10
+  # permgen: 10
   stack: 5
   native: 10