Use `bash` instead of `sh` in README and build.sh (#2)

`build.sh` uses bash-specific array creation syntax, which may not
work with `/bin/sh`. Change it to `bash` to avoid confusion:

README.md

@@ -40,17 +40,17 @@ OceanBase Database is under [MulanPubL - 2.0](https://license.coscl.org.cn/Mulan
 
 ### debug mode
 ```sh
-sh build.sh debug --init --make
+bash build.sh debug --init --make
 ```
 
 ### release mode
 ```sh
-sh build.sh release --init --make
+bash build.sh release --init --make
 ```
 
 ### rpm packages
 ```sh
-sh build.sh rpm --init && cd build_rpm && make -j16 rpm
+bash build.sh rpm --init && cd build_rpm && make -j16 rpm
 ```
 
 ## Contributing

build.sh

-#!/bin/sh
+#!/bin/bash
 TOPDIR="$(dirname $(readlink -f "$0"))"
 BUILD_SH=${TOPDIR}/build.sh
 DEP_DIR=${TOPDIR}/deps/3rd/usr/local/oceanbase/deps/devel