Switch to the supported VS 2015 environment in AppVeyor (#748)
Switch to the supported VS 2015 environment in AppVeyor (#748)

We were using an unstable environment.

victorporof/tofino,jsantell/tofino,mozilla/tofino,victorporof/tofino,bgrins/tofino,mozilla/tofino,jsantell/tofino,mozilla/tofino,bgrins/tofino,bgrins/tofino,bgrins/tofino,mozilla/tofino,jsantell/tofino,jsantell/tofino