If you haven't updated to the latest version of git take a look at this SO post on installing Git on CentOS also take a look at the full post here for installing fish on other OS'
# switch back with 'su - vagrant' or preferred user when needed
sudo -i
cd /etc/yum.repos.d/
# install wget
yum -y install wget
# for CentOS 7
wget http://download.opensuse.org/repositories/shells:fish:release:2/CentOS_7/shells:fish:release:2.repo
# Update and upgrade the system:
yum repolist
yum update
# Install fish
yum -y install fish
# Install omf
curl -L https://get.oh-my.fish | fish