Fix a configuration error detected on macosx with --use_vulkan --embed_kernels

me:~/RadeonRays_SDK$ ./Tools/premake/osx/premake5 --use_vulkan --embed_kernels
>> Vulkan backend enabled
** Warning: the flags value Symbols has been deprecated.
   Use `symbols "On"` instead
Traceback (most recent call last):
  File "../Tools/scripts/stringify.py", line 29, in <module>
    files = os.listdir(dir)
OSError: [Errno 2] No such file or directory: '/Users/me/RadeonRays_SDK/RadeonRays./../RadeonRays/src/kernels/GLSL/'
>> RadeonRays: VK kernels embedded
Type 'premake5 --help' for help

Author: Gjacquenot

RadeonRays/RadeonRays.lua

@@ -72,7 +72,7 @@ project "RadeonRays"
 
         if _OPTIONS["use_vulkan"] then
             os.execute( "python ../Tools/scripts/stringify.py " ..
-                                os.getcwd() .. "./../RadeonRays/src/kernels/GLSL/ "  ..
+                                os.getcwd() .. "/../RadeonRays/src/kernels/GLSL/ "  ..
                                 ".comp " ..
                                 "vulkan " ..
                                  "> ./src/kernelcache/kernels_vk.h"