fix doc typo

one can find correct name of variable just few lines below the typo
Merge pull request #13195 from budnik/patch-1

fix doc typo
Gruntfile.js: Remove default `report` option.
Add TOC entry for "Third-party libraries" callout section to JS docs
Change GA events to Universal Analytics
Revert upgrade to Universal Analytics

The Google Analytics account we use cannot currently be upgraded to Universal Analytics. In order to keep using Analytics, we have to stick with Classic for now.