[build] Use MSVS 2015 by default.

gni/isolate.gni

 # Copyright 2016 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/sanitizers/sanitizers.gni")
 import("//third_party/icu/config.gni")
 import("v8.gni")
 
 declare_args() {
   # Sets the test isolation mode (noop|prepare|check).
@@ skipping 144 matching lines @@
         "target_arch=$target_arch",
         "--config-variable",
         "v8_use_external_startup_data=$use_external_startup_data",
         "--config-variable",
         "v8_use_snapshot=$use_snapshot",
       ]
 
       if (is_win) {
         args += [
           "--config-variable",
-          "msvs_version=2013",
+          "msvs_version=2015",
         ]
       } else {
         args += [
           "--config-variable",
           "msvs_version=0",
         ]
       }
     }
   }
 }