Use std::make_unique when possible

We've required C++14 for a while now. As we're mostly C with a little
C++, this is less helpful, but may as well avoid bare new where
possible.

Change-Id: Icf3386e3f3b6f2092bb0089ed874cc50985f1a40
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/61429
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

tool/digest.cc

diff --git a/tool/digest.cc b/tool/digest.cc
index d810928..e66f013 100644
--- a/tool/digest.cc
+++ b/tool/digest.cc
@@ -115,7 +115,7 @@
   }
 
   static const size_t kBufSize = 8192;
-  std::unique_ptr<uint8_t[]> buf(new uint8_t[kBufSize]);
+  auto buf = std::make_unique<uint8_t[]>(kBufSize);
 
   bssl::ScopedEVP_MD_CTX ctx;
   if (!EVP_DigestInit_ex(ctx.get(), md, NULL)) {