Update link to qelib1.inc file (#7508)

The link to the OpenQASM file `qelib1.inc`, mentioned in this notebook,
seems to have changed since the time this was written.

Author: mhucka

docs/build/interop.ipynb

@@ -333,7 +333,7 @@
    "source": [
     "#### Gate conversion rules \n",
     "\n",
-    "Note: The standard Quantum Experience gates (defined in [qelib.inc](https://github.com/Qiskit/qiskit-terra/blob/master/qiskit/qasm/libs/qelib1.inc)) are \n",
+    "Note: The standard Quantum Experience gates (defined in [qelib1.inc](https://github.com/Qiskit/qiskit/blob/50523425cb469b0e0268f39b05b20816d703c7e2/qiskit/qasm/libs/qelib1.inc)) are \n",
     "based on the `U` and `CX` built-in instructions, and we could generate them dynamically. Instead, we chose to map them to native Cirq gates explicitly, which results in a more user-friendly circuit. \n",
     "\n",
     "| QE gates| Cirq translation| Notes|\n",