fix doc ports

Author: joamatab

.github/write_cells_si220.py

@@ -60,7 +60,7 @@
 
   import cspdk
 
-  c = cspdk.si220.cells.{name}({kwargs})
+  c = cspdk.si220.cells.{name}({kwargs}).dup()
   c.draw_ports()
   c.plot()
 

.github/write_cells_si500.py

@@ -60,7 +60,7 @@
 
   import cspdk
 
-  c = cspdk.si500.cells.{name}({kwargs})
+  c = cspdk.si500.cells.{name}({kwargs}).dup()
   c.draw_ports()
   c.plot()
 

.github/write_cells_sin300.py

@@ -60,7 +60,7 @@
 
   import cspdk
 
-  c = cspdk.si220.cells.{name}({kwargs})
+  c = cspdk.si220.cells.{name}({kwargs}).dup()
   c.draw_ports()
   c.plot()