fix typo error (#1387)

ppocr/metrics/cls_metric.py

@@ -32,9 +32,8 @@ class ClsMetric(object):
 
     def get_metric(self):
         """
-        return metircs {
-                 'acc': 0,
-                 'norm_edit_dis': 0,
+        return metrics {
+                 'acc': 0
             }
         """
         acc = self.correct_num / self.all_num

ppocr/metrics/det_metric.py

@@ -57,7 +57,7 @@ class DetMetric(object):
 
     def get_metric(self):
         """
-        return metircs {
+        return metrics {
                  'precision': 0,
                  'recall': 0,
                  'hmean': 0

ppocr/metrics/rec_metric.py

@@ -43,7 +43,7 @@ class RecMetric(object):
 
     def get_metric(self):
         """
-        return metircs {
+        return metrics {
                  'acc': 0,
                  'norm_edit_dis': 0,
             }