use portable shebangs consistently

.hooks/pre-commit.sh

@@ -1,3 +1,3 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 make

scripts/doc-comments.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 out=$(grep -nr "^--- @" lua)
 

scripts/help-update.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 # run after changing nvim-tree.lua DEFAULT_OPTS or keymap.lua M.default_on_attach
 # scrapes and updates nvim-tree-lua.txt

scripts/luals-check.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 # Performs a lua-language-server check on all files.
 # luals-out/check.json will be produced on any issues, returning 1.