added <cmath> for Mac

python/sentencepiece.i

@@ -2,6 +2,7 @@
 %include exception.i
 
 %{
+#include <cmath>
 #include <sentencepiece_processor.h>
 #include <sentencepiece_trainer.h>
 

python/sentencepiece_wrap.cxx

@@ -3119,6 +3119,7 @@ namespace swig {
 }
 
 
+#include <cmath>
 #include <sentencepiece_processor.h>
 #include <sentencepiece_trainer.h>