Fix make fails in minimal alpine-bash + make (SeleniumHQ#961)

* Fix make fails in minimal alpine-bash + make

Complete/standard call hides the problem a bit:
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bash-5.0# make generate_all
cd ./Hub && ./generate.sh 3.141.59-titanium selenium SeleniumHQ
cd ./NodeBase && ./generate.sh 3.141.59-titanium selenium SeleniumHQ
/bin/sh: ./generate.sh: not found
make: *** [Makefile:39: generate_nodebase] Error 127
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Step-by-step:
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bash-5.0# cd NodeBase/
bash-5.0# ./generate.sh 3.141.59-titanium selenium SeleniumHQ
bash: ./generate.sh: /bin/bash: bad interpreter: No such file or directory
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* Fix make fails in minimal alpine-bash + make

* Fix make fails in minimal alpine-bash + make

Author: reinholdfuereder

NodeBase/generate.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 VERSION=$1
 NAMESPACE=$2
 AUTHORS=$3

NodeChrome/generate.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 VERSION=$1
 NAMESPACE=$2
 AUTHORS=$3

NodeFirefox/generate.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 VERSION=$1
 NAMESPACE=$2
 AUTHORS=$3