Refer to error_code with the std prefix.

git-svn-id: svn://svn.chromium.org/llvm-project/cfe/trunk/tools/clang-format@210817 0b72dbe1-c17f-4bc7-b9db-2b4152be0356
diff --git a/ClangFormat.cpp b/ClangFormat.cpp
index 189a611..e023949 100644
--- a/ClangFormat.cpp
+++ b/ClangFormat.cpp
@@ -210,7 +210,7 @@
       new DiagnosticOptions);
   SourceManager Sources(Diagnostics, Files);
   std::unique_ptr<MemoryBuffer> Code;
-  if (error_code ec = MemoryBuffer::getFileOrSTDIN(FileName, Code)) {
+  if (std::error_code ec = MemoryBuffer::getFileOrSTDIN(FileName, Code)) {
     llvm::errs() << ec.message() << "\n";
     return true;
   }