Fix typo

PINNs_1DHeatEquationExample.ipynb

@@ -21,7 +21,7 @@
     "\n",
     "This notebook is based on two papers: *[Physics-Informed Neural Networks:  A Deep Learning Framework for Solving Forward and Inverse Problems Involving Nonlinear Partial Differential Equations](https://www.sciencedirect.com/science/article/pii/S0021999118307125)* and *[Hidden Physics Models:  Machine Learning of Nonlinear Partial Differential Equations](https://www.sciencedirect.com/science/article/pii/S0021999117309014)* with the help of  Fergus Shone and Michael Macraild.\n",
     "\n",
-    "These tutorials will go through solving Partial Differential Equations using Physics Informed Neuaral Networks, focusing on the 1D Heat Equation and a more complex example using the Navier Stokes Equations.\n",
+    "These tutorials will go through solving Partial Differential Equations using Physics Informed Neural Networks, focusing on the 1D Heat Equation and a more complex example using the Navier Stokes Equations.\n",
     "\n",
     "**This introduction section is replicated in all PINN tutorial notebooks (please skip if you've already been through).** \n",
     "\n",