fix(R): Fix swig build by hiding python specifics

Author: danieledler

interfaces/swig/Infomap.i

@@ -45,5 +45,6 @@ namespace std {
 /* Parse the header file to generate wrappers */
 %include "src/Infomap.h"
 
-
+#ifdef SWIGPYTHON
 %pythoncode "interfaces/python/infomap.py"
+#endif