Rename variable to not include the VS version

This minimizes the number of changes when the tool has to target a
higher version of Visual Studio. Besides, it doesn't actually point
to Visual Studio per-se.

Author: Immo Landwerth

build.cmd

@@ -4,9 +4,9 @@ SETLOCAL
 
 SET CACHED_NUGET=%LocalAppData%\NuGet\NuGet.exe
 SET SOLUTION_PATH=%~dp0src\CodeFormatter.sln
-SET VS2015_BUILD_TOOLS_PATH="%ProgramFiles(x86)%\MSBuild\14.0\bin\MSBuild.exe"
+SET BUILD_TOOLS_PATH="%ProgramFiles(x86)%\MSBuild\14.0\bin\MSBuild.exe"
 
-IF NOT EXIST %VS2015_BUILD_TOOLS_PATH% (
+IF NOT EXIST %BUILD_TOOLS_PATH% (
   echo In order to build or run this tool you need either Visual Studio 2015 Preview or
   echo Microsoft Build Tools 2015 Preview tools installed.
   echo.