[SQLLINE-287] Support JDK 12

Document JDK 12 as our preferred JDK version; anything as old as JDK 8
is fine.

Use JDK 12 to build releases, and add JDK 12 to the list of JDKs to
test each release on.

Enable Travis on JDK 12. (Also enable Travis on JDK 13, which is still
under development.)

Enable AppVeyor on JDK 12.

.travis.yml

@@ -3,6 +3,8 @@ language: java
 matrix:
  fast_finish: true
  include:
+ - env: IMAGE=maven:3-jdk-13
+ - env: IMAGE=maven:3-jdk-12
  - env: IMAGE=maven:3-jdk-11 JDOC=Y
  - env: IMAGE=maven:3-jdk-10
  - env: IMAGE=maven:3-jdk-9

HOWTO.md

@@ -11,8 +11,8 @@ Capitalization is tricky:
 ## How to make a release (for committers)
 
 Make sure `mvn clean install`, `mvn site`, and
-`mvn javadoc:javadoc javadoc:test-javadoc` pass under JDK 8, 9, 10 and
-11.
+`mvn javadoc:javadoc javadoc:test-javadoc` pass under JDK 8, 9, 10,
+11 and 12.
 
 Write release notes. Run the
 [relNotes](https://github.com/julianhyde/share/blob/master/tools/relNotes)
@@ -21,7 +21,7 @@ script and append the output to [HISTORY.md](HISTORY.md).
 Update version numbers in README, README.md, src/docbkx/manual.xml,
 and the copyright date in NOTICE.
 
-Switch to JDK 11.
+Switch to JDK 12.
 
 Check that the sandbox is clean:
 

README.md

@@ -125,7 +125,7 @@ Use the following definition to use `sqlline` in your maven project:
 Prerequisites:
 
 * Maven 3.2.5 or higher
-* Java 8 or higher (10 preferred)
+* Java 8 or higher (12 preferred)
 
 Check out and build:
 

appveyor.yml

@@ -19,6 +19,7 @@ environment:
  - JAVA_HOME: C:\Program Files\Java\jdk9
  - JAVA_HOME: C:\Program Files\Java\jdk10
  - JAVA_HOME: C:\Program Files\Java\jdk11
+ - JAVA_HOME: C:\Program Files\Java\jdk12
 build_script:
 - mvn clean -V install -DskipTests -Dmaven.javadoc.skip=true -Djavax.net.ssl.trustStorePassword=changeit
 test_script: