Bugfix: Swap order of datediff input fields in performance timing page view context

[vlambertgrove]

Description & motivation

While doing some debugging on the snowplow performance timing at Grove, I noticed that the jinja for this code was reversed from what the original data model has:

https://github.com/snowplow/snowplow-web-data-model/blob/master/redshift/sql/01-page-views/05-timing-context.sql#L83-L85

The effect of this is that when the three timestamps are 0 (representing ok values) rather than large negative numbers there are large positive numbers. This causes records to be filtered erroneously.

Swapping the order in the datediffs should be enough to resolve the bug.

Checklist

• I have verified that these changes work locally
• I have updated the README.md (if applicable)
• I have added tests & descriptions to my models (and macros if applicable)

[leahwicz]

@jtcohen6 I'm approving this b/c it looks right to me but you made the change a year ago here that flipped them so if there was a reason, lets review this when you get back
https://github.com/dbt-labs/snowplow/pull/89/files

[jtcohen6]

@leahwicz You're totally right... I don't think I had meant to do that!

Thanks for the fix @vlambertgrove! This looks good to merge. I'll follow up by cutting a patch release of the package (v0.13.1).