The version information basically uses 20 characters for date and time,
which is small enough to specify an arbitrary version string. Therefore,
increase the buffer a little.
The idea is to have something like EXTRAVERSION. This is useful for
getting RC tags, development tags and for customizing the version. For
example using the tag `nuttx-10.0.0-RC0` the VERSION will be
`10.0.0-RC0`
Signed-off-by: Matheus Castello <matheus@castello.eng.br>
