Fix month slider ticks in the 311 data portal

[eclee25]

Examine the interface of the 311 data portal.

Update the R Shiny app (technically, the slider will be modified in Javascipt in prettify_slider.js) to remove extraneous tick marks in all of the month sliders. There should be one tick per month.

Input:
Fork the repo available here

Output:
Updated R Shiny app code

When you are finished
Submit a pull request on GitHub (eclee25/the-rat-hack repo), or upload your scripts.
Upload any files to Dropbox

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