a mistake at step 'Install site'

Help me please. When you install drupal-8.2.5 such a mistake at step ‘Install site’

Error
The website encountered an unexpected error. Please try again later.
RuntimeException: Failed to start the session because headers have already been sent by “/home/africatr/orafricatravel.com/docs/new/core/lib/Drupal/Core/Database/Database.php” at line 289. in SymfonyComponentHttpFoundationSessionStorageNativeSessionStorage->start() (line 140 of vendor/symfony/http-foundation/Session/Storage/NativeSessionStorage.php).
SymfonyComponentHttpFoundationSessionStorageNativeSessionStorage->start() (Line: 163)
DrupalCoreSessionSessionManager->startNow() (Line: 194)
DrupalCoreSessionSessionManager->save() (Line: 181)
SymfonyComponentHttpFoundationSessionSession->save() (Line: 620)
install_run_task(Array, Array) (Line: 538)
install_run_tasks(Array) (Line: 115)
install_drupal(Object) (Line: 44)

what should I do?

Drupal version: 


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