Fix coordinate vector sizes in TRAPPING binary I/O

src/trapping/cfrfme.cpp

@@ -278,7 +278,7 @@ void frfme(string data_file, string output_path) {
 	  tfrfme.write(reinterpret_cast<char *>(&nkv), sizeof(int));
 	  tfrfme.write(reinterpret_cast<char *>(&nxv), sizeof(int));
 	  tfrfme.write(reinterpret_cast<char *>(&nyv), sizeof(int));
-	  tfrfme.write(reinterpret_cast<char *>(&nxv), sizeof(int));
+	  tfrfme.write(reinterpret_cast<char *>(&nzv), sizeof(int));
 	  tfrfme.write(reinterpret_cast<char *>(&vk), sizeof(double));
 	  tfrfme.write(reinterpret_cast<char *>(&exri), sizeof(double));
 	  tfrfme.write(reinterpret_cast<char *>(&an), sizeof(double));