feat: use env for POSIX compliance on silly Mac systems

src/script/webgraph_ranking/graph_explore_build_vertex_map.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Build node indexes to interactively explore a Common Crawl webgraph.
 # The webgraph files are expected to be placed in the current directory.

src/script/webgraph_ranking/graph_explore_download_webgraph.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 NAME="$1"
 if ! shift 1; then