make __file__ an absolute path (for Linux+python 3.8)

fossils.py

@@ -286,6 +286,8 @@ if __name__ == "__main__":
     os.environ['OMP_NUM_THREADS'] = str(args.k)
     cxxfem.set_num_threads(args.k)
 
+    __file__ = os.path.abspath(__file__) # relative path on Linux with python <=3.8
+
     # display env variables
     try:
         print(f"OMP_NUM_THREADS={os.environ['OMP_NUM_THREADS']}")