Source: http://ir.tesla.com/common/download/download.cfm?companyid=A...
Edit: fixed link to correct source, as pointed out below. In this pdf, it's on bottom of page 3, under "Outlook".
Edit: I guess you mean this one: http://files.shareholder.com/downloads/ABEA-4CW8X0/200707627...
That does indeed say 20,000. They actually produced 18,345, for a miss of about 8%. They ramped up production from about 1,000 cars/week to 2,000 cars/week, so being short 1,655 indicates that their production ramp-up was delayed by about 10 days. Doesn't seem like a very big deal to me, and a slight miss of estimated production increases is way different from the "sales are down, Tesla is doomed" that got reported.
[1] http://insideevs.com/teslas-2nd-production-line-capable-pump...
Here's a long video of the assembly process in 2015.[1] This is useful, rather than the usual quick montage of cool robot scenes. There was a surprising amount of manual assembly in areas where other manufacturers are automated.