Ket formatting revisions and typo fix (#654)

* Fixed ket formatting

* Fixed typo

Author: MatthewGregoire42

qiskit/terra/operators_overview.ipynb

@@ -175,7 +175,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "If the input matrix is not divisible into qubit subsystems then it will be stored as a single qudit operator. For example if we have a 6 x 6 matrix:"
+    "If the input matrix is not divisible into qubit subsystems then it will be stored as a single qubit operator. For example if we have a 6 x 6 matrix:"
    ]
   },
   {
@@ -929,7 +929,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.7"
+   "version": "3.6.8"
   }
  },
  "nbformat": 4,