Change "that's if" to "that if"

01_intro.ipynb

@@ -263,7 +263,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Harvard professor David Perkins, who wrote Making Learning Whole, has much to say about teaching. The basic idea is to teach the *whole game*. That means that's if you're teaching baseball, you first take people to a baseball game or get them to play it. You don't teach them how to line thread into a ball, the physics of a parabola, or the coefficient of friction of a ball on a bat.\n",
+    "Harvard professor David Perkins, who wrote Making Learning Whole, has much to say about teaching. The basic idea is to teach the *whole game*. That means that if you're teaching baseball, you first take people to a baseball game or get them to play it. You don't teach them how to line thread into a ball, the physics of a parabola, or the coefficient of friction of a ball on a bat.\n",
     "\n",
     "Paul Lockhart, a Columbia math PhD, former Brown professor, and K-12 math teacher, imagines in the influential essay A Mathematician's Lament a nightmare world where music and art are taught the way math is taught. Children would not be allowed to listen to or play music until they have spent over a decade mastering music notation and theory, spending classes transposing sheet music into a different key. In art class, students study colours and applicators, but aren't allowed to actually paint until college. Sound absurd? This is how math is taught–we require students to spend years doing rote memorization, and learning dry, disconnected *fundamentals* that we claim will pay off later, long after most of them quit the subject.\n",
     "\n",