Win32: Fix value for _WIN32_WINNT_WINBLUE

An incorrect value for _WIN32_WINNT_WINBLUE caused GLFW to think Windows
8 was 8.1 or greater.  This led to a crash when attempting to call
SetProcessDpiAwareness.

Closes #1775.

src/win32_platform.h

@@ -102,7 +102,7 @@
  #define DISPLAY_DEVICE_ACTIVE 0x00000001
 #endif
 #ifndef _WIN32_WINNT_WINBLUE
- #define _WIN32_WINNT_WINBLUE 0x0602
+ #define _WIN32_WINNT_WINBLUE 0x0603
 #endif
 #ifndef _WIN32_WINNT_WIN8
  #define _WIN32_WINNT_WIN8 0x0602