version.sh: fix typo

Signed-off-by: Sergei Trofimovich <slyfox@inbox.ru>

maint/version.sh

@@ -36,7 +36,7 @@ saved_version=
 [ -z "${saved_version}" -o "${saved_version}" != "${new_version}" ] && {
     cat >${VERSION_FILE} <<EOF
 #ifndef MC_CURRENT_VERSION
-/* This is autogenerated file. Don't edit! */
+/* This is an autogenerated file. Don't edit! */
 #define MC_CURRENT_VERSION "${new_version}"
 #endif
 EOF