fix shell match to account for /usr/local for homebrew installs of zsh on macOS

paper

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 
 # resolve shell-specifics
-case "$(echo "$SHELL" | sed 's|/usr||g')" in
+case "$(echo "$SHELL" | sed -E 's|/usr(/local)?||g')" in
     "/bin/zsh")
         RCPATH="$HOME/.zshrc"
         SOURCE="${BASH_SOURCE[0]:-${(%):-%N}}"