Whitelist `tsv` extension when opening CSV files

Fixes #429

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com)
 and this project adheres to [Semantic Versioning](https://semver.org).
 
+## [Unreleased]
+
+### Fixed
+
+- Whitelist `tsv` extension when opening CSV files [#429](https://github.com/PHPOffice/PhpSpreadsheet/issues/429)
+
 ## [1.7.0] - 2019-05-26
 
 ### Added

src/PhpSpreadsheet/Reader/Csv.php

@@ -545,7 +545,8 @@ class Csv extends BaseReader
         fclose($this->fileHandle);
 
         // Trust file extension if any
-        if (strtolower(pathinfo($pFilename, PATHINFO_EXTENSION)) === 'csv') {
+        $extension = strtolower(pathinfo($pFilename, PATHINFO_EXTENSION));
+        if (in_array($extension, ['csv', 'tsv'])) {
             return true;
         }