There are two easy ways to fix your problem:
use pushd/popd
Just change current folder inside the default-config files and restore afterwards:
pushd ~/.dot-files/bash/
source ./.alias
source ./.prompt
source ./.zsh-git-info
source ./.git-prompt.sh
popd
Of course, your default-config files would differ in this one line.
use variable
Define a variable inside .bashrc and .zshrc. The variable will point to where your sourced files are:
# .bashr
fdir=~/.dot-files/bash
source "${fdir}/default-config"
Do the same for .zshrc
And inside the default-config can be the same for both shells, just reuse this variable:
source "${fdir}/.alias"
source "${fdir}/.prompt"
source "${fdir}/.zsh-git-info"
source "${fdir}/.git-prompt.sh"
