Explicitly export the scala version

Author: ningyougang

.travis.yml

@@ -27,6 +27,7 @@ env:
   global:
     - ANSIBLE_CMD="ansible-playbook -i environments/local -e docker_image_prefix=testing"
     - GRADLE_PROJS_SKIP=""
+    - OW_SCALA_VERSION=2.13
 
 notifications:
   email: false
@@ -66,6 +67,7 @@ install:
 jobs:
   include:
     - script:
+        - export OW_SCALA_VERSION=2.13
         - TERM=dumb OW_SCALA_VERSION=2.13 ./gradlew :tests:compileTestScala
       name: "Scala 2.13 compilation"
     - script: