refactor

[  8%] Building CXX object src/main/CMakeFiles/main.dir/Spawnables.cpp.o
/app/src/main/Spawnables.cpp: In member function 'Spawnables::const_iterator Spawnables::erase(Spawnables::const_iterator)':
/app/src/main/Spawnables.cpp:12:32: error: no matching function for call to 'std::list<std::pair<int, Spawnable*> >::erase(Spawnables::const_iterator&)'
     return items.erase(iterator);
                                ^
/app/src/main/Spawnables.cpp:12:32: note: candidates are:
In file included from /usr/include/c++/4.8/list:64:0,
                 from /app/src/main/Spawnables.h:7,
                 from /app/src/main/Spawnables.cpp:1:
/usr/include/c++/4.8/bits/list.tcc:108:5: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator) [with _Tp = std::pair<int, Spawnable*>; _Alloc = std::allocator<std::pair<int, Spawnable*> >; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<std::pair<int, Spawnable*> >]
     list<_Tp, _Alloc>::
     ^
/usr/include/c++/4.8/bits/list.tcc:108:5: note:   no known conversion for argument 1 from 'Spawnables::const_iterator {aka std::_List_const_iterator<std::pair<int, Spawnable*> >}' to 'std::list<std::pair<int, Spawnable*> >::iterator {aka std::_List_iterator<std::pair<int, Spawnable*> >}'
In file included from /usr/include/c++/4.8/list:63:0,
                 from /app/src/main/Spawnables.h:7,
                 from /app/src/main/Spawnables.cpp:1:
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note: std::list<_Tp, _Alloc>::iterator std::list<_Tp, _Alloc>::erase(std::list<_Tp, _Alloc>::iterator, std::list<_Tp, _Alloc>::iterator) [with _Tp = std::pair<int, Spawnable*>; _Alloc = std::allocator<std::pair<int, Spawnable*> >; std::list<_Tp, _Alloc>::iterator = std::_List_iterator<std::pair<int, Spawnable*> >]
       erase(iterator __first, iterator __last)
       ^
/usr/include/c++/4.8/bits/stl_list.h:1193:7: note:   candidate expects 2 arguments, 1 provided
/app/src/main/Spawnables.cpp:13:1: error: control reaches end of non-void function [-Werror=return-type]
 }
 ^
cc1plus: all warnings being treated as errors
make[2]: *** [src/main/CMakeFiles/main.dir/Spawnables.cpp.o] Error 1
make[1]: *** [src/main/CMakeFiles/main.dir/all] Error 2
make: *** [all] Error 2