Fix compilation with nvcc 10.1.

[syoyo]

This PR fixes compilation with nvcc 10.1 (it looks nvcc 10.1 does not like using namespace)

$ nvcc --version
nvcc: NVIDIA (R) Cuda compiler driver
Copyright (c) 2005-2019 NVIDIA Corporation
Built on Sun_Jul_28_19:07:16_PDT_2019
Cuda compilation tools, release 10.1, V10.1.243

$ nvcc -arch=sm_70 -std=c++11 -O2  -Iwaveglow/header/ -Icommon/header -Isys/header -o common/obj/logger.o -c common/src/logger.cpp -D DEBUG
common/src/logger.cpp:9:6: error: explicit specialization of ‘template<class T> void livai::tts::common::log(const string&, const T&)’ outside its namespace must use a nested-name-specifier [-fpermissive]
 void log<std::vector<size_t>>(const std::string& name, const std::vector<size_t>& obj)
      ^~~~~~~~~~~~~~~~~~~~~~~~