[Refactor] Add indexes to personal_access_tokens (#571)

* Add Indexing to p_a_t

* Update 2019_12_14_000001_create_personal_access_tokens_table.php

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Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: keshav-k3

database/migrations/2019_12_14_000001_create_personal_access_tokens_table.php

@@ -18,7 +18,7 @@ public function up(): void
             $table->string('token', 64)->unique();
             $table->text('abilities')->nullable();
             $table->timestamp('last_used_at')->nullable();
-            $table->timestamp('expires_at')->nullable();
+            $table->timestamp('expires_at')->nullable()->index();
             $table->timestamps();
         });
     }