fuzz/minimise_corpora.sh: Add shebang and chmod +x

The script now matches fuzz/refresh_ssl_corpora.sh.

Change-Id: I0089c5091e3e21c5590a73909b05e066fefe4a34
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/47604
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/fuzz/minimise_corpora.sh b/fuzz/minimise_corpora.sh
old mode 100644
new mode 100755
index 7c45ef6..6567141
--- a/fuzz/minimise_corpora.sh
+++ b/fuzz/minimise_corpora.sh
@@ -1,3 +1,4 @@
+#!/bin/bash
 # Copyright (c) 2016, Google Inc.
 #
 # Permission to use, copy, modify, and/or distribute this software for any