Add missing algorithm include

[ogasser]

Fixes the following error during compilation:

patricia.cpp: In member function ‘int Patricia::parsePrefix(int, char*, std::string*)’:
patricia.cpp:1028:21: error: ‘remove_if’ is not a member of ‘std’; did you mean ‘remove_cv’?
 1028 |     line.erase(std::remove_if(line.begin(), line.end(), isspace), line.end());
      |                     ^~~~~~~~~
      |                     remove_cv
make[2]: *** [Makefile:650: patricia.o] Error 1