Rename precision_recall_curve.png bug fix (#1431)

* fix error in train.py line 400, changed precision-recall_curve.png to precision_recall_curve.png and fix error in test.py of {wandb.init() before wandb.log()} by importing wand and initializing it before wand.log()

* Update test.py

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

train.py

@@ -397,7 +397,7 @@ def train(hyp, opt, device, tb_writer=None, wandb=None):
             plot_results(save_dir=save_dir)  # save as results.png
             if wandb:
                 wandb.log({"Results": [wandb.Image(str(save_dir / x), caption=x) for x in
-                                       ['results.png', 'precision-recall_curve.png']]})
+                                       ['results.png', 'precision_recall_curve.png']]})
         logger.info('%g epochs completed in %.3f hours.\n' % (epoch - start_epoch + 1, (time.time() - t0) / 3600))
     else:
         dist.destroy_process_group()