message: fix directory that is used to extract UE engine
diff: @@ -9,6 +9,7 @@ then
  elif [[ $TRAVIS_OS_NAME == "osx" ]]
  then
  AWS_ACCESS_KEY_ID=${GOOGLE_ACCESS_KEY_ID} AWS_SECRET_ACCESS_KEY=${GOOGLE_SECRET_ACCESS_KEY} aws s3 --endpoint-url https://storage.googleapis.com cp s3://cesium-unreal-engine/macos-2021-04-13/UE_4.26.tar.gz .
  - tar xfz UE_4.26.tar.gz -C $HOME
  + mkdir $HOME/UE_4.26
  + tar xfz UE_4.26.tar.gz -C $HOME/UE_4.26
  rm UE_4.26.tar.gz
  fi
  