Update install.sh (#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: NLogan Adams <114770087+loadams@users.noreply.github.com>
Co-authored-by: NOlatunji Ruwase <olruwase@microsoft.com>

install.sh

-#!/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
 }