travis config on 2.6.x (#4916)

Author: beiwei30

.travis.yml

@@ -9,9 +9,6 @@ matrix:
         - ZULUJDK=7
 
 before_install:
-  # installing the rpm package
-  - sudo apt-get update -qq
-  - sudo apt-get install -qq rpm
   # adding $HOME/.sdkman to cache would create an empty directory, which interferes with the initial installation
   - "[[ -d $HOME/.sdkman/bin/ ]] || rm -rf $HOME/.sdkman/"
   - curl -sL https://get.sdkman.io | bash
@@ -31,4 +28,4 @@ script:
   - travis_wait 30 ./mvnw clean install -DskipTests=false -Dcheckstyle.skip=false -Drat.skip=false -Dmaven.javadoc.skip=true
 
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)