[Fix] `nvm_normalize_lts`: switch from expr to case

avoids `expr: warning: ^lts/-[1-9][0-9]*: using ^ as the first character of a basic regular expression is not portable; it is ignored`

nvm.sh

@@ -756,10 +756,16 @@ nvm_normalize_lts() {
   local LTS
   LTS="${1-}"
 
-  if [ "$(expr "${LTS}" : '^lts/-[1-9][0-9]*$')" -gt 0 ]; then
+  case "${LTS}" in
+    lts/-[123456789] | lts/-[123456789][0123456789]*)
       local N
       N="$(echo "${LTS}" | cut -d '-' -f 2)"
       N=$((N+1))
+      # shellcheck disable=SC2181
+      if [ $? -ne 0 ]; then
+        nvm_echo "${LTS}"
+        return 0
+      fi
       local NVM_ALIAS_DIR
       NVM_ALIAS_DIR="$(nvm_alias_path)"
       local RESULT
@@ -770,9 +776,11 @@ nvm_normalize_lts() {
         nvm_err 'That many LTS releases do not exist yet.'
         return 2
       fi
-  else
+    ;;
+    *)
       nvm_echo "${LTS}"
-  fi
+    ;;
+  esac
 }
 
 nvm_ensure_version_prefix() {