clang-format-vs : Fix typo NUGET_EXE_DIR on README

[empty2fill]

Summary

Match with the CMake variable.

[hans]

Thanks!

Do you have commit access, or if not would you like me to commit on your behalf?

[empty2fill]

In D70632#1758572, @hans wrote:

Thanks!

Do you have commit access, or if not would you like me to commit on your behalf?

Commit on my behalf please. Thank you.

clang/tools/clang-format-vs/README.txt

 This directory contains a VSPackage project to generate a Visual Studio extension
 for clang-format.
 
 Build prerequisites are:
 - Visual Studio 2015
 - Extensions SDK (you'll be prompted to install it if you open ClangFormat.sln)
 
 The extension is built using CMake to generate the usual LLVM.sln by setting
 the following CMake vars:
 
 - BUILD_CLANG_FORMAT_VS_PLUGIN=ON
 
-- NUGET_EXE_PATH=path/to/nuget_dir (unless nuget.exe is already available in PATH)
+- NUGET_EXE_DIR=path/to/nuget_dir (unless nuget.exe is already available in PATH)
 
 example:
   cd /d C:\code\llvm
   mkdir build & cd build
-  cmake -DBUILD_CLANG_FORMAT_VS_PLUGIN=ON -DNUGET_EXE_PATH=C:\nuget ..
+  cmake -DBUILD_CLANG_FORMAT_VS_PLUGIN=ON -DNUGET_EXE_DIR=C:\nuget ..
 
 Once LLVM.sln is generated, build the clang_format_vsix target, which will build
 ClangFormat.sln, the C# extension application.
 
 The CMake build will copy clang-format.exe and LICENSE.TXT into the ClangFormat/
 directory so they can be bundled with the plug-in, as well as creating
 ClangFormat/source.extension.vsixmanifest. Once the plug-in has been built with
 CMake once, it can be built manually from the ClangFormat.sln solution in Visual