Update Chp_02.ipynb

[rvcoile]

correction so the posterior integrates to unity

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[olszewskip]

An analogous change could/should be made in solutions 2M[1-2] to this chapter.

[canyon289]

hi @rvcoile, can you run precommit pre-commit run --all-files to update these files? It'll get the notebook up the same standard as the rest automagically

https://github.com/pymc-devs/resources/runs/5618658061?check_suite_focus=true#step:4:83