Summary: Brilliant adds "Probability" course

Why It Matters: This change adds a new math topic for learners.

What Changed:

• "Log in" changed to "Sign in"
• "Interactive problem solving" changed to "Learn by doing"
• "Graphs and Functions" changed to "Functions"
• Added "Probability" to Math Courses
• Removed "Calculus" from Math Courses
• Added "Free learning videos" under Product
• Removed "and Linear Algebra" from "Vectors and Linear Algebra"