[Robustness] avoid a clobbered `ls`

Fixes #2824

nvm.sh

@@ -1880,7 +1880,7 @@ nvm_get_arch() {
   # change ARCH to 32bit ARM (armv7l) if /sbin/init is 32bit executable
   local L
   if [ "$(uname)" = "Linux" ] && [ "${NVM_ARCH}" = arm64 ] &&
-    L="$(ls -dl /sbin/init 2>/dev/null)" &&
+    L="$(command ls -dl /sbin/init 2>/dev/null)" &&
     [ "$(od -An -t x1 -j 4 -N 1 "${L#*-> }")" = ' 01' ]; then
     NVM_ARCH=armv7l
     HOST_ARCH=armv7l