title: what's difference about git branch -d <branchname> and git branch -D <branchname>
body: <p>I an newer about git. after I merge my branch from another branch, I found something wrong. Now my status is I have commit these changes from merging, but not push into the origin/mybranch. So I just wanna delete my local branch. Then I use git branch -d mybranch. However, it failed. It told me that I cann't delete my local branch. After searching goolge, I found the command git branch -D mybranch, and used it to delete my branch successfully. So could anyone told the difference about these two commands ?</p>