Make macos_allow_gatekeeper a bit safer

Removed an extra newline and ensured it runs in the script directory
regardless of the working directory.

tools/vargo/src/main.rs

@@ -1162,11 +1162,12 @@ fn run() -> Result<(), String> {
             let mut dependency_missing = false;
 
             let mut macos_prepare_script = format!(
-                r#"
-#!/bin/bash
+                r#"#!/bin/bash
 set -e
 set -x
 
+cd "$( dirname "${{BASH_SOURCE[0]}}" )"
+
 "#
             );
             use std::fmt::Write;