Use /usr/bin/env in bash and python script shebangs

bin/regen-protos.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e
 
@@ -12,4 +12,4 @@ cd proto
 
 #echo "Regenerating protobuf documentation - if you see an error message"
 #echo "you can ignore it unless doing a new protobuf release to github."
-#bin/regen-docs.sh
+#bin/regen-docs.sh