Fixed RCE in git grep.

A specific option in git grep could be added inside the
pattern to be searched for, resulting in possible RCE.

Thanks to Kacper Szurek (https://security.szurek.pl) for
catching this one!

tests/RepositoryTest.php

@@ -0,0 +1,28 @@
+<?php
+
+use GitList\Git\Client;
+use GitList\Git\Repository;
+use PHPUnit\Framework\TestCase;
+use Prophecy\Argument;
+
+class RepositoryTest extends TestCase
+{
+    public function testIsSanitizingSearchWithPager()
+    {
+        $client = $this->prophesize(Client::class);
+        $client->run(Argument::type(Repository::class), "grep -i --line-number -- '=sleep 5;' master")->shouldBeCalled();
+
+        $repository = new Repository('/tmp', $client->reveal());
+        $repository->searchTree('--open-files-in-pager=sleep 5;', 'master');
+        $repository->searchTree('-O=sleep 5;', 'master');
+    }
+
+    public function testIsSanitizingSearchWithAnyOption()
+    {
+        $client = $this->prophesize(Client::class);
+        $client->run(Argument::type(Repository::class), "grep -i --line-number -- 'foobar  =bar;' foo")->shouldBeCalled();
+
+        $repository = new Repository('/tmp', $client->reveal());
+        $repository->searchTree('foobar --bar --foo=bar;', 'foo');
+    }
+}