Add null coalesce operator in token count vectoriezer

src/Phpml/FeatureExtraction/TokenCountVectorizer.php

@@ -132,7 +132,7 @@ class TokenCountVectorizer implements Transformer
             return false;
         }
 
-        return isset($this->vocabulary[$token]) ? $this->vocabulary[$token] : false;
+        return $this->vocabulary[$token] ?? false;
     }
 
     /**

src/Phpml/Metric/ClassificationReport.php

@@ -163,7 +163,7 @@ class ClassificationReport
             return 0.0;
         }
 
-        return 2.0 * (($precision * $recall) / ($divider));
+        return 2.0 * (($precision * $recall) / $divider);
     }
 
     /**