Updates default version to 15.7 for next release.
Updates default version to 15.7 for next release.

zooba/PTVS,Microsoft/PTVS,int19h/PTVS,int19h/PTVS,zooba/PTVS,Microsoft/PTVS,huguesv/PTVS,int19h/PTVS,int19h/PTVS,zooba/PTVS,Microsoft/PTVS,zooba/PTVS,zooba/PTVS,Microsoft/PTVS,huguesv/PTVS,int19h/PTVS,huguesv/PTVS,int19h/PTVS,huguesv/PTVS,huguesv/PTVS,huguesv/PTVS,zooba/PTVS,Microsoft/PTVS,Microsoft/PTVS