Fixed #105.

[inetfuture]

Use '-M' to force rename branch when setup git in deploying process, otherwise, git will throw error: 'fatal: A branch named 'master' already exists.' if 'config.branch' is 'master' and therefore later process will fail.

[inetfuture]

Actually, it's not about #105, I misidentified it. This commit solved this problem:

root@aaron-desktop:/home/aaron/workspace/blog# hexo deploy
Setting up.
Initialized empty Git repository in /home/aaron/workspace/blog/.deploy/.git/
[master (root-commit) bfd5a5b] First commit
 0 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 placeholder
fatal: A branch named 'master' already exists.