Update gn documentation for --ide=vs.

The default is VS 2017 as of 7295a84e468138d53fc1f2259d737768f52e803c.

Bug: 683729
Change-Id: I795011162e0a9f6c39af799b50d32587b0baed76
Reviewed-on: https://chromium-review.googlesource.com/821211
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#523274}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c851ab862aaf3d893863cf5a6150d8bf0a22e52a
diff --git a/tools/gn/command_gen.cc b/tools/gn/command_gen.cc
index 67ac18a..ca65877 100644
--- a/tools/gn/command_gen.cc
+++ b/tools/gn/command_gen.cc
@@ -304,7 +304,7 @@
       Generate files for an IDE. Currently supported values:
       "eclipse" - Eclipse CDT settings file.
       "vs" - Visual Studio project/solution files.
-             (default Visual Studio version: 2015)
+             (default Visual Studio version: 2017)
       "vs2013" - Visual Studio 2013 project/solution files.
       "vs2015" - Visual Studio 2015 project/solution files.
       "vs2017" - Visual Studio 2017 project/solution files.
diff --git a/tools/gn/docs/reference.md b/tools/gn/docs/reference.md
index 18985f1..3f931fb 100644
--- a/tools/gn/docs/reference.md
+++ b/tools/gn/docs/reference.md
@@ -633,7 +633,7 @@
       Generate files for an IDE. Currently supported values:
       "eclipse" - Eclipse CDT settings file.
       "vs" - Visual Studio project/solution files.
-             (default Visual Studio version: 2015)
+             (default Visual Studio version: 2017)
       "vs2013" - Visual Studio 2013 project/solution files.
       "vs2015" - Visual Studio 2015 project/solution files.
       "vs2017" - Visual Studio 2017 project/solution files.