chore: upgrade bigtable samples to v2 (#2012)

Author: bshaffer

bigtable/composer.json

@@ -1,6 +1,6 @@
 {
     "require": {
-        "google/cloud-bigtable": "^1.30"
+        "google/cloud-bigtable": "^2.0"
     },
     "autoload-dev": {
         "psr-4": {

bigtable/src/hello_world.php

@@ -127,7 +127,7 @@
 $columnFamilyId = 'cf1';
 
 $row = $table->readRow($key, [
-    'rowFilter' => $rowFilter
+    'filter' => $rowFilter
 ]);
 printf('%s' . PHP_EOL, $row[$columnFamilyId][$column][0]['value']);
 // [END bigtable_hw_get_with_filter]