besseres build script

build.bat

@@ -1,12 +1,12 @@
 :DebugLinux64
 SET RETURN=DebugLinux64
 SET NEXT=ReleaseLinux64
-"%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" "Erhaltung Server.sln" /t:rebuild /p:configuration=debug /p:platform=x64
+"%InstallDir%\%MSBuildExe%" "Erhaltung Server.sln" /t:rebuild /p:configuration=debug /p:platform=x64
 if errorlevel 1 GOTO Error
 :ReleaseLinux64
 SET RETURN=ReleaseLinux64
 SET NEXT=End
-"%InstallDir%\MSBuild\15.0\Bin\MSBuild.exe" "Erhaltung Server.sln" /t:rebuild /p:configuration=release /p:platform=x64
+"%InstallDir%\%MSBuildExe%" "Erhaltung Server.sln" /t:rebuild /p:configuration=release /p:platform=x64
 if errorlevel 1 GOTO Error
 GOTO End
 :Error