fix ubuntu build

csrc/cpu/ego_sample_cpu.cpp

 #include "ego_sample_cpu.h"
 
 #include <ATen/Parallel.h>
-#include <process.h>
 
 #include "utils.h"
 
+#ifdef _WIN32
+#include <process.h>
+#endif
+
 inline torch::Tensor vec2tensor(std::vector<int64_t> vec) {
   return torch::from_blob(vec.data(), {(int64_t)vec.size()}, at::kLong).clone();
 }

csrc/cpu/hgt_sample_cpu.cpp

 #include "hgt_sample_cpu.h"
 
-#include <process.h>
-
 #include "utils.h"
 
+#ifdef _WIN32
+#include <process.h>
+#endif
+
 #define MAX_NEIGHBORS 50
 
 using namespace std;

csrc/cpu/neighbor_sample_cpu.cpp

 #include "neighbor_sample_cpu.h"
 
-#include <process.h>
-
 #include "utils.h"
 
+#ifdef _WIN32
+#include <process.h>
+#endif
+
 using namespace std;
 
 namespace {

csrc/cpu/sample_cpu.cpp

 #include "sample_cpu.h"
 
-#include <process.h>
-
 #include "utils.h"
 
+#ifdef _WIN32
+#include <process.h>
+#endif
+
 // Returns `rowptr`, `col`, `n_id`, `e_id`
 std::tuple<torch::Tensor, torch::Tensor, torch::Tensor, torch::Tensor>
 sample_adj_cpu(torch::Tensor rowptr, torch::Tensor col, torch::Tensor idx,