Use /bin/bash in run_tests.sh.

I got this error:
./run_tests.sh: 42: ./run_tests.sh: Syntax error: "(" unexpected

nsock/tests/run_tests.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 # nsock regression test suite
 # Same license as nmap -- see http://nmap.org/book/man-legal.html