Add bash >= v4.0 check

bonsai.sh

@@ -42,6 +42,12 @@ nfetch=0
 changed=()
 seed="$RANDOM"
 
+# ensure Bash version >= 4.0
+ver="$(printf '%s' "$BASH_VERSION" | cut -d . -f 1)"
+if [ -z "$ver" ] || [ "$ver" -lt 4 ]; then
+	printf '%s\n' "Error: requires Bash v4.0 or higher. You have version $BASH_VERSION."
+fi
+
 # ensure MacOS compatibility with GNU getopt
 if [[ "$OSTYPE" == 'darwin'* ]]; then
     GGETOPT=/usr/local/Cellar/gnu-getopt/*/bin/getopt # should find gnu-getopt