fix slow bash startup from overuse of brew --prefix

custompkg/root/etc/skel/Library/bashrc.d/200.git-prompt.sh

@@ -1,5 +1,7 @@
-if [ -f "$(brew --prefix bash-git-prompt)/share/gitprompt.sh" ]; then
+BGPPREFIX="$HOME/Library/Homebrew/opt/bash-git-prompt"
+
+if [ -f "$BGPPREFIX/share/gitprompt.sh" ]; then
   GIT_PROMPT_THEME=Default
   GIT_PROMPT_ONLY_IN_REPO=1
-  source "$(brew --prefix bash-git-prompt)/share/gitprompt.sh"
+  source "$BGPPREFIX/share/gitprompt.sh"
 fi