Fix undefined reference to parseNumberFromStringWithBase<int>

[LilMouse]

Could not build with scons. It gave the error

src/bsontools/hex.o: In function `_bson::Status _bson::parseNumberFromString<int>(_bson::StringData const&, int*)':
hex.cpp:(.text+0x4c2): undefined reference to `_bson::Status _bson::parseNumberFromStringWithBase<int>(_bson::StringData const&, int, int*)'

By adding dep1 hex target the issue is resolved.