Switch to focal (Ubuntu 20.04)

Add pip3 update

Author: VolkerHartmann

.travis.yml

@@ -1,6 +1,6 @@
 language: java
 
-dist: xenial
+dist: focal
 
 jdk:
 # Enable all versions which should be supported
@@ -13,6 +13,7 @@ before_install:
 - docker pull elasticsearch:7.9.3
 - docker run -d --name elasticsearch4metastore  -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" elasticsearch:7.9.3
 - sudo apt-get install --assume-yes python3 python3-pip 
+- pip3 install --upgrade pip
 - pip3 install xmltodict wget
 
 install: true