We currently have to put the c++ version in two place, (1) [common.gypi](https://github.com/mapbox/node-cpp-skel/blob/5383586d35e38138ebf4b05cb3307839a2c1db25/common.gypi#L5) and (2) [binding.gyp](https://github.com/mapbox/node-cpp-skel/blob/5383586d35e38138ebf4b05cb3307839a2c1db25/binding.gyp#L110): Let's add a shared variable for c++ version that we can use in these two places.
We currently have to put the c++ version in two place, (1) common.gypi and (2) binding.gyp:
Let's add a shared variable for c++ version that we can use in these two places.