Move hash bang to first line.

For hash bang statements to take effect, they must be the first line
in a script.

Fixes #953.

run_in_docker.sh

@@ -1,3 +1,5 @@
+#!/bin/bash
+
 # Copyright 2018 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -12,7 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-#!/bin/bash
 set -e
 
 if [ $# -lt 3 ]; then