leveldb: Include <algorithm> in util/env_test.cc.

CL 170738066 introduced std::min and std::max to env_test.cc. These
require the <algorithm> header.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171024062

util/env_test.cc

@@ -4,6 +4,8 @@
 
 #include "leveldb/env.h"
 
+#include <algorithm>
+
 #include "port/port.h"
 #include "util/testharness.h"
 #include "util/testutil.h"