Yes, you still have to have insurance.
Source (in German, sorry)
Basically it says you have to be insured if:
- you take up residence in Switzerland
- you are issued a Swiss work permit valid for three months or more
- you work in Switzerland for less than three months, but your insurance from home does not cover everything that the Swiss basic policy does
- other cases too, but these are the most relevant bits. There's a list of exceptions afterward but none of them apply to your situation.