silence pointer arithmetic warning issued for !GDL.RELEASE string trim

[GillesDuvert]

Compilation produces

initsysvar.cpp:659:58: warning: adding 'int' to a string does not append to the string [-Wstring-plus-int]
gdlStruct->NewTag("RELEASE", new DStringGDL( VERSION + (VERSION[0] == 'v' ? 1 : 0)));

I do not see the point of doing this, so I leave it as it is....

[slayoo]

Thanks @GillesDuvert for reporting.
I've introduced it here: #1780
The idea is to strip the leading "v" in the C string (char*) VERSION by adding one to the pointer.
git describe returns the tag name which in most cases starts with "v" (like v1.0.0), but we expect !GDL.RELEASE to be 1.0.1