Modernize: use null coalesce

There's bound to be more places where this can be used, but this was the only one I've come across in the past six months which was an obvious one.

Author: jrfnl

src/Generators/Text.php

@@ -220,15 +220,8 @@ private function linesToTableRows(array $column1Lines, array $column2Lines)
 
         $rows = '';
         for ($i = 0; $i < $maxLines; $i++) {
-            $column1Text = '';
-            if (isset($column1Lines[$i]) === true) {
-                $column1Text = $column1Lines[$i];
-            }
-
-            $column2Text = '';
-            if (isset($column2Lines[$i]) === true) {
-                $column2Text = $column2Lines[$i];
-            }
+            $column1Text = ($column1Lines[$i] ?? '');
+            $column2Text = ($column2Lines[$i] ?? '');
 
             $rows .= '| ';
             $rows .= $column1Text.str_repeat(' ', max(0, (47 - strlen($column1Text))));