Use #!/usr/bin/env bash instead of #!/bin/bash (#254)

Refer to https://github.com/dylanaraps/pure-bash-bible#shebang

substrate/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 # This script assumes that all pre-requisites are installed.
 

substrate/ci/publish-wasm.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Publish wasm binaries into the special repository.
 # This script assumes that wasm binaries have already been built.

substrate/ci/script.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 set -eux
 

substrate/common.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 ROOT=`dirname "$0"`
 

substrate/demo/runtime/wasm/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 cargo +nightly build --target=wasm32-unknown-unknown --release

substrate/init.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e
 

substrate/polkadot/parachain/test-chains/basic_add/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 # Make LLD produce a binary that imports memory from the outside environment.

substrate/polkadot/parachain/test-chains/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 rm -rf ./target

substrate/polkadot/runtime/wasm/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 cargo +nightly build --target=wasm32-unknown-unknown --release

substrate/substrate/executor/wasm/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 cargo +nightly build --target=wasm32-unknown-unknown --release

substrate/substrate/test-runtime/wasm/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 cargo +nightly build --target=wasm32-unknown-unknown --release

substrate/update-genesis.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 cp polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm polkadot/runtime/wasm/genesis.wasm