PhyisiCell_rules.o typo is corrected

Makefile

@@ -42,7 +42,7 @@ BioFVM_utilities.o BioFVM_basic_agent.o BioFVM_MultiCellDS.o BioFVM_agent_contai
 
 PhysiCell_core_OBJECTS := PhysiCell_phenotype.o PhysiCell_cell_container.o PhysiCell_standard_models.o \
 PhysiCell_cell.o PhysiCell_custom.o PhysiCell_utilities.o PhysiCell_constants.o PhysiCell_basic_signaling.o \
-PhysiCell_signal_behavior.o PhyisiCell_rules.o
+PhysiCell_signal_behavior.o PhysiCell_rules.o
 
 PhysiCell_module_OBJECTS := PhysiCell_SVG.o PhysiCell_pathology.o PhysiCell_MultiCellDS.o PhysiCell_various_outputs.o \
 PhysiCell_pugixml.o PhysiCell_settings.o PhysiCell_geometry.o