update to java 11 ubuntu code example

Example: how to upgrade java 8 to 11 in ubuntu

sudo apt-get install openjdk-11-jdk

$ sudo update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).

Selection    Path                                            Priority   Status

* 0            /usr/lib/jvm/java-9-openjdk-amd64/bin/java       1500      auto mode
  1            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1500      manual mode
  2            /usr/lib/jvm/java-9-openjdk-amd64/bin/java       1500      manual mode