dlopen correctly - leave out Linux version suffix

Index: external/imgui/imgui_impl_opengl3_loader.h
--- external/imgui/imgui_impl_opengl3_loader.h.orig
+++ external/imgui/imgui_impl_opengl3_loader.h
@@ -662,7 +662,7 @@ static GL3WglProc (*glx_get_proc_address)(const GLubyt
 
 static int open_libgl(void)
 {
-    libgl = dlopen("libGL.so.1", RTLD_LAZY | RTLD_LOCAL);
+    libgl = dlopen("libGL.so", RTLD_LAZY | RTLD_LOCAL);
     if (!libgl)
         return GL3W_ERROR_LIBRARY_OPEN;
     *(void **)(&glx_get_proc_address) = dlsym(libgl, "glXGetProcAddressARB");
