Update install.sh (deepspeedai#3270)

Optimization Code
1. Use #!/usr/bin/env bash instead of #!/bin/bash to make the script more portable.
2. Use rm -rf instead of rm -r to remove directories recursively.

Co-authored-by: Logan Adams <[email protected]>
Co-authored-by: Olatunji Ruwase <[email protected]>

Author: 3 people

install.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e
 err_report() {
@@ -121,7 +121,7 @@ rm_if_exist() {
     if [ -f $1 ]; then
         rm $VERBOSE $1
     elif [ -d $1 ]; then
-        rm -r $VERBOSE $1
+        rm -rf $VERBOSE $1
     fi
 }