Fix implicit narrowing error in initializer list

The implicit narrowing in the initializer list throws a compiler error for some compilers with C++11 support turned on. The specific error message is: "error: narrowing conversion of 'PyInt_AsLong(((PyObject*)o))' from 'long int' to 'double' inside { }".

Tested on Clang 5.1.0 and Mac OS X 10.9.4.