Fixed prerender detection (fixes #391)
Fixed prerender detection (fixes #391)

snowplow/snowplow-javascript-tracker,juliomenendez/snowplow-javascript-tracker,snowplow/snowplow-javascript-tracker,snowplow/snowplow-javascript-tracker,juliomenendez/snowplow-javascript-tracker,snowplow/snowplow-javascript-tracker,YieldifyLabs/snowplow-javascript-tracker,YieldifyLabs/snowplow-javascript-tracker,YieldifyLabs/snowplow-javascript-tracker,juliomenendez/snowplow-javascript-tracker