.gitignore过滤当前目录下的文件夹，不影响其他目录

$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean

log/

/log

$ git status
On branch master
Your branch is up to date with 'origin/master'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   .gitignore

Untracked files:
  (use "git add <file>..." to include in what will be committed)

        src/main/java/sysu/newchain/consensus/pbft/msg/log/

no changes added to commit (use "git add" and/or "git commit -a")