[clang-tools-extra] Migrate llvm::make_unique to std::make_unique

Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.

Differential revision: https://reviews.llvm.org/D66259

llvm-svn: 368944
diff --git a/clang-tools-extra/clangd/JSONTransport.cpp b/clang-tools-extra/clangd/JSONTransport.cpp
index 1731077..4921035 100644
--- a/clang-tools-extra/clangd/JSONTransport.cpp
+++ b/clang-tools-extra/clangd/JSONTransport.cpp
@@ -294,7 +294,7 @@
                                             llvm::raw_ostream *InMirror,
                                             bool Pretty,
                                             JSONStreamStyle Style) {
-  return llvm::make_unique<JSONTransport>(In, Out, InMirror, Pretty, Style);
+  return std::make_unique<JSONTransport>(In, Out, InMirror, Pretty, Style);
 }
 
 } // namespace clangd