Fixed kicad2step not loading 3D models (bizarre case)

- If we saved the PCB to /tmp and then we reverted the changes to
  use the PCB the KIPRJMOD environment var pointed to the temporal.
- KiCad defines it during Save and Python becomes unsync, so we
  can't even notice it!

Fixes #186

kibot/out_step.py

@@ -82,6 +82,10 @@ class STEPOptions(Base3DOptions):
         cmd, video_remove = add_extra_options(cmd)
         # Execute and inform is successful
         logger.debug('Executing: '+str(cmd))
+        # Ensure KIPRJMOD is correct:
+        # KiCad sets KIPRJMOD each time we call BOARD.Save() but then Python `os.environ` becomes unsynchronized
+        # We don't even know the actual value and any call to Save could destroy it
+        os.environ['KIPRJMOD'] = os.path.dirname(board_name)
         try:
             cmd_output = check_output(cmd, stderr=STDOUT)
         except CalledProcessError as e: