Adjust latest to 13 and remove 12 (now EOL)

See https://jdk.java.net/12/:

> The JDK 12 Early Access Program has concluded.

Author: tianon

.appveyor.yml

@@ -7,8 +7,6 @@ environment:
       variant: windowsservercore-ltsc2016
     - version: 13
       variant: windowsservercore-ltsc2016
-    - version: 12
-      variant: windowsservercore-ltsc2016
     - version: 11
       variant: windowsservercore-ltsc2016
     - version: 8

.travis.yml

@@ -15,11 +15,6 @@ matrix:
     - os: windows
       dist: 1803-containers
       env: VERSION=13 VARIANT=windows/windowsservercore-1803
-    - os: linux
-      env: VERSION=12 VARIANT=oracle
-    - os: windows
-      dist: 1803-containers
-      env: VERSION=12 VARIANT=windows/windowsservercore-1803
     - os: linux
       env: VERSION=11
     - os: linux

12/jdk/oracle/Dockerfile

@@ -2,8 +2,8 @@
 set -Eeuo pipefail
 
 declare -A aliases=(
-	[12-jdk]='jdk latest'
-	[12-jre]='jre'
+	[13-jdk]='jdk latest'
+	[13-jre]='jre'
 )
 defaultType='jdk'