title: Cannot compile nms_cuda in mmdetection using colaboratory
body: <pre><code>/usr/local/lib/python3.6/dist-packages/torch/include/ATen/core/TensorBody.h:262:30: note: declared here
     DeprecatedTypeProperties &amp; type() const {
                                ^~~~
  mmdet/ops/nms/src/nms_cuda.cpp:4:23: error: ‘AT_CHECK’ was not declared in this scope
   #define CHECK_CUDA(x) AT_CHECK(x.type().is_cuda(), #x, " must be a CUDAtensor ")
                         ^
  mmdet/ops/nms/src/nms_cuda.cpp:4:23: note: in definition of macro ‘CHECK_CUDA’
   #define CHECK_CUDA(x) AT_CHECK(x.type().is_cuda(), #x, " must be a CUDAtensor ")
                         ^~~~~~~~
  mmdet/ops/nms/src/nms_cuda.cpp:4:23: note: suggested alternative: ‘DCHECK’
   #define CHECK_CUDA(x) AT_CHECK(x.type().is_cuda(), #x, " must be a CUDAtensor ")
                         ^
  mmdet/ops/nms/src/nms_cuda.cpp:4:23: note: in definition of macro ‘CHECK_CUDA’
   #define CHECK_CUDA(x) AT_CHECK(x.type().is_cuda(), #x, " must be a CUDAtensor ")
                         ^~~~~~~~
  error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
  </code></pre>
  
  <p>Now all the info I get:</p>
  
  <ul>
  <li>sys.version 8.2</li>
  <li>/usr/bin/gcc 7</li>
  <li>gcc versio 7.5</li>
  </ul>
  
  <p>Is it normal? 
  What happened? Cuda error? gcc error?
  How to solve. I'm hurried to use it to run mmdetection program.</p>