Update imports in iv_pymc notebook

Replaces import of LinearRegression from causalpy.skl_models with sklearn's LinearRegression and removes execution count from the first code cell.

Author: drbenvincent

docs/source/notebooks/iv_pymc.ipynb

@@ -12,7 +12,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -21,11 +21,11 @@
     "import numpy as np\n",
     "import pandas as pd\n",
     "from matplotlib.lines import Line2D\n",
+    "from sklearn.linear_model import LinearRegression as sk_lin_reg\n",
     "\n",
     "import causalpy as cp\n",
     "from causalpy import InstrumentalVariable\n",
-    "from causalpy.pymc_models import InstrumentalVariableRegression\n",
-    "from causalpy.skl_models import LinearRegression as sk_lin_reg"
+    "from causalpy.pymc_models import InstrumentalVariableRegression"
    ]
   },
   {