Test against all python versions since JAVA 8 is now working on xenial.

.travis.yml

@@ -4,12 +4,11 @@ language: python
 
 python:
   - '3.5'
- # - '3.6'
- # - '3.7'
+  - '3.6'
+  - '3.7'
 
 env:
   - ENV_STRING=pandas0.24.1
-    JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
 #  - ENV_STRING=pandas0.24.0
 #
 #  - ENV_STRING=pandas0.23.4
@@ -33,21 +32,19 @@ env:
 #  - ENV_STRING=pandas0.19.0
 #
   - ENV_STRING=pyspark2.4.0
-    JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
 #  - ENV_STRING=pyspark2.3.1
 
 
 dist: xenial
 
 before_install:
-  - java -version
-  - echo $JAVA_HOME
-  - export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
   - sudo add-apt-repository -y ppa:openjdk-r/ppa
   - sudo apt-get -qq update
   - sudo apt-get install -y openjdk-8-jdk --no-install-recommends
   - sudo update-java-alternatives -s java-1.8.0-openjdk-amd64
   - java -version
+  - echo $JAVA_HOME
+  - export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
 
 install:
   - echo $JAVA_HOME