Update quickstart.ipynb

Fixed a typo

docs/notebooks/quickstart.ipynb

@@ -1262,7 +1262,7 @@
    "source": [
     "## Devices with multiple films\n",
     "\n",
-    "In this example we model a an on-chip flux bias line (in layer ``W0``), which is partially covered by a shield in another layer (``W1``). We use ``SuperScreen`` to calculate the mutual inductance between the bias line and a pickup loop which also lies in ``W0``. Both layers are assumed to have a London penetration depth of 100 nm and thickness of 50 nm, and the vertical spacing between the layers is 250 nm."
+    "In this example we model an on-chip flux bias line (in layer ``W0``), which is partially covered by a shield in another layer (``W1``). We use ``SuperScreen`` to calculate the mutual inductance between the bias line and a pickup loop which also lies in ``W0``. Both layers are assumed to have a London penetration depth of 100 nm and thickness of 50 nm, and the vertical spacing between the layers is 250 nm."
    ]
   },
   {