Fixing missing <limits> include

Fixed the following issue while compiling:
Consolidate compiler generated dependencies of target riss-lib-object
[ 21%] Building CXX object riss/CMakeFiles/riss-lib-object.dir/utils/SimpleGraph.cc.o
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc: In member function ‘std::vector<double> SimpleGraph::getDistances(int)’:
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:365:52: error: ‘numeric_limits’ was not declared in this scope
  365 |     for (int x = 0; x < size; x++) { distance[x] = numeric_limits<double>::infinity(); } //distance to all nodes = inf
      |                                                    ^~~~~~~~~~~~~~
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:365:67: error: expected primary-expression before ‘double’
  365 |     for (int x = 0; x < size; x++) { distance[x] = numeric_limits<double>::infinity(); } //distance to all nodes = inf
      |                                                                   ^~~~~~
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc: In member function ‘double SimpleGraph::getRadius()’:
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:410:21: error: ‘numeric_limits’ was not declared in this scope
  410 |     double radius = numeric_limits<double>::infinity();
      |                     ^~~~~~~~~~~~~~
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:410:36: error: expected primary-expression before ‘double’
  410 |     double radius = numeric_limits<double>::infinity();
      |                                    ^~~~~~
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc: In member function ‘double SimpleGraph::getExzentricity(int)’:
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:427:28: error: ‘numeric_limits’ was not declared in this scope
  427 |         if (distance[j] == numeric_limits<double>::infinity()) { continue; }
      |                            ^~~~~~~~~~~~~~
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:427:43: error: expected primary-expression before ‘double’
  427 |         if (distance[j] == numeric_limits<double>::infinity()) { continue; }
      |                                           ^~~~~~
/home/soos/development/sat_solvers/riss/riss/utils/SimpleGraph.cc:427:43: error: expected ‘)’ before ‘double’
  427 |         if (distance[j] == numeric_limits<double>::infinity()) { continue; }
      |            ~                              ^~~~~~
      |                                           )
make[2]: *** [riss/CMakeFiles/riss-lib-object.dir/build.make:181: riss/CMakeFiles/riss-lib-object.dir/utils/SimpleGraph.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:323: riss/CMakeFiles/riss-lib-object.dir/all] Error 2
make: *** [Makefile:136: all] Error 2
conp-solutions / riss

Fixing missing <limits> include #17
