[Tests] blacklist expired LetsEncrypt CA

workaround for TravisCI's ubuntu 16.04

.travis.yml

@@ -14,6 +14,8 @@ cache:
     - $TRAVIS_BUILD_DIR/.cache
     - $TRAVIS_BUILD_DIR/node_modules
 before_install:
+  - sudo sed -i 's/mozilla\/DST_Root_CA_X3.crt/!mozilla\/DST_Root_CA_X3.crt/g' /etc/ca-certificates.conf
+  - sudo update-ca-certificates -f
   - $SHELL --version 2> /dev/null || dpkg -s $SHELL 2> /dev/null || which $SHELL
   - curl --version
   - wget --version