Updated episode 4 refs

Author: abraham.asfaw

Coding_With_Qiskit/ep4_Gates.ipynb

@@ -323,7 +323,7 @@
     "\n",
     "https://github.com/Qiskit/qiskit-iqx-tutorials\n",
     "\n",
-    "For a pedagogical presentation of the Bra-Ket notation and the matrix algebra involved in quantum circuits, check out our open-source `Learning Quantum Computation using Qiskit` textbook:\n",
+    "For a pedagogical presentation of the Bra-Ket notation and the matrix algebra involved in quantum circuits, check out our open-source `Learn Quantum Computation using Qiskit` textbook:\n",
     "\n",
     "https://community.qiskit.org/textbook/\n",
     "\n",