Fix shebang lines for a few scripts

On the BSDs, bash is typically installed in /usr/local/bin.

Signed-off-by:	Shawn Webb <shawn.webb@hardenedbsd.org>

scripts/copy-katex-assets

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -Eeuo pipefail
 
 echo "Copying katex assets into bundle directory"

scripts/install-binaries

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 REPO_ROOT=$(git rev-parse --show-toplevel 2>/dev/null || echo "$PWD")

scripts/install-twemoji-assets

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -Eeou pipefail
 
 version="$(node -e 'console.log(require("twemoji/package.json").version)')"