Remove bad space character (#4020)

Replaces "NARROW NO-BREAK SPACE" with regular "SPACE". This type of
space produces a warning when building our application. We had a similar
instance months ago in #3426

Author: arnaucasau

learning/courses/quantum-machine-learning/data-encoding.ipynb

@@ -121,7 +121,7 @@
     "\n",
     "These bit strings are assigned to three sets of four qubits, so the overall 12-qubit basis state is:\n",
     "$$\n",
-    "∣0101 0111 0000⟩\n",
+    "∣0101 0111 0000⟩\n",
     "$$\n",
     "\n",
     "Here, the first four qubits represent the first feature, the next four qubits the second feature, and the last four qubits the third feature. The code below converts the data vector (5,7,0) to a quantum state, and is generalized to do so for other single-digit features."