Redash visualizations not rendering for some number types

[emtwo]

Here are two examples of graphs that did not work until the columns were cast to varchar:

https://sql.telemetry.mozilla.org/queries/47041/source#127382
https://sql.telemetry.mozilla.org/queries/52474#139768

[irrationalagent]

I also had to cast to varchar for x-axis variables (that were ints). similar plots didn't require this before the facelift

[tdsmith]

I suspect the substr call in this commit isn't handling numerical axes: eb1b3cb#diff-11830b1c2a93941fe75a5bef8246c00aR234

[tdsmith]

Thanks!

[madalincm]

Verified as fixed in FF59(win7) in stmo-stage using the test queries from #378

Marking bug as verified fixed.

[jezdez]

@emtwo 🙏 🏆 🎉