Subtract 1 from months when making JavaScript Dates for use in Google charts

[srowen]

Subtract 1 from months when making JavaScript Dates for use in Google charts. JS months are 0-indexed.

Description of changeset:

I believe this resolves #278
This seems to be the jinja2 way of subtracting from a variable's value:
http://jinja.pocoo.org/docs/2.10/templates/#math

Test Plan:

./run-tests.sh passes. I admit I'm not sure how to run the locally built copy of knowledge repo to check the change.

Auto-reviewers: @NiharikaRay @matthewwardrop @earthmancash @danfrankj

[AppVeyorBot]

✅ Build knowledge-repo 1.0.621 completed (commit 0d9f055420 by @srowen)

[matthewwardrop]

@srowen Thanks for this patch as well! It looks good. Should the day also be zero-indexed?

[srowen]

Thanks again for the tip on running locally @matthewwardrop . Yes it seems to fix the display issue.
No only months are 0-indexed: https://www.w3schools.com/js/js_date_methods.asp
This mirrors Java FWIW.

[matthewwardrop]

@srowen This patch looks good also. I'll merge it in. Thanks for fixing these papercut issues.

Thanks also for being thorough and for the JS reference. I've done quite a bit of JS work myself in other projects, including work with dates, but always end up having to check the idiosyncrasies of each datetime library lest I make these off-by-one errors (like this one, though at least this one in particular was not of my hand ;).

[srowen]

Thanks! just little things indeed but help our internal usage at Databricks, where it's pretty helpful. Maybe I can add our org to INTHEWILD.md

[matthewwardrop]

@srowen Feel free to add your org to the INTHEWILD.md file :). Glad it is useful to you!