Suggestion of changing the commands to install and update a plugin

I suggest run this command to install a plugin:
`git clone -b master --single-branch --depth 1 {repo}`
This command to update a plugin:
`git fetch --depth 1 origin master && git reset --hard @{u}`

Explanation:
1. We don't need to download history commits, so `--single-branch --depth 1` is better.
2. The plugin folders are not supposed to be touched by user. Therefore, `reset --hard` is better than `pull` as sometimes `pull` doesn't work because of local changes by any reasons.