We don't need to run CI when the master branch is updated. Skip it.
Note: If a user created a PR to the master branch, %APPVEYOR_REPO_BRANCH% will be set to "master". To skip only the master branch, we need to check that %APPVEYOR_PULL_REQUEST_HEAD_REPO_BRANCH% is undefined.
Currently, CI is executed twice every day:
We don't need to run CI when the master branch is updated. Skip it.
Note: If a user created a PR to the master branch, %APPVEYOR_REPO_BRANCH% will be set to "master". To skip only the master branch, we need to check that %APPVEYOR_PULL_REQUEST_HEAD_REPO_BRANCH% is undefined.