Fixed cert errors with travis and oracleJDK

.travis.yml

@@ -2,5 +2,13 @@ language: java
 jdk:
   - oraclejdk9
   - openjdk8
+
+matrix:
+  include:
+  - jdk: openjdk9
+    before_install:
+    - rm "${JAVA_HOME}/lib/security/cacerts"
+    - ln -s /etc/ssl/certs/java/cacerts "${JAVA_HOME}/lib/security/cacerts"
+    
 after_success:
   - mvn clean test jacoco:report coveralls:report