Explicit requirements.txt location (#4225)

val.py

@@ -320,7 +320,7 @@ def parse_opt():
 def main(opt):
     set_logging()
     print(colorstr('val: ') + ', '.join(f'{k}={v}' for k, v in vars(opt).items()))
-    check_requirements(exclude=('tensorboard', 'thop'))
+    check_requirements(requirements=FILE.parent / 'requirements.txt', exclude=('tensorboard', 'thop'))
 
     if opt.task in ('train', 'val', 'test'):  # run normally
         run(**vars(opt))