Fixed formatting in t-test examples

[tanishy7777]

Formatted the docs for t-test for better readability, by adding a line break to distinguish between the consecutive steps.

Before
$\beta_0 + \epsilon_i = \beta_0 + \beta_1 + \epsilon_i\ 0 = \beta_1 $

After
$\beta_0 + \epsilon_i = \beta_0 + \beta_1 + \epsilon_i\ $
$\beta_1 = 0 $

Fixes #860

• code passes black
• code passes pylint
• all tests pass

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[tomicapretto]

Thanks!