add overflow-y: hidden to mathjax containers

[thehappycheese]

closes #674

Adds overflow-y:hidden to the mathjax container template CSS.

This removes unnesisary vertical scroll bars that show up in Chrome and Edge when overflow-x is set to auto, particularly for multi-line display mode math blocks.

Click Here to expand source code for images below

test_module.py:

r"""
# Inline math tests

this is an $i=n$ line math expression

# Single line display mode

Long (always needs horizontal scroll)

$$
5a^3b^2 - 2b^4c + 7c^2d^3e - 3d^2ef^2 + 6e^3f - 4a^2f^3 + 9a^4bc^2 - 8b^3d^2e^2 + 3c^5de - 7d^3e^4f + 2a^2b^2c^3 - 6b^5df^2 + 4c^3d^4e^2 - 9d^2e^3f^3 + 5a^3cf^4 - 2b^2d^5e + 8c^4d^2f - 6a^5be^3 + 7b^3c^2d^3
$$

Short (never needs scroll)

$$
5a^3b^2 - 2b^4c + 7c^2d^3e - 3d^2ef^2
$$

# Multi line display mode

$$
\\begin{align}
2x^2 + 3y - 7z &= 5 \\\\
11 &= 4x - 6y^3 + 2z^2 + 5a^3b^2 - 2b^4c + 7c^2d^3e - 3d^2ef^2 + 6e^3f - 4a^2f^3 \\\\
9x^3 - 5y^2 + z &= 3
\\end{align}
$$

"""

Before

After

[mhils]

Thanks! 🍰