CNBC host Jim Cramer has advised investors to sell their shares in Chinese electric vehicle maker Nio Inc. and buy shares in Tesla Inc. instead.What Happened: On the CNBC “Mad Money" lightning round,Cramer saidinvestors in Nio should be switching to Tesla, as it is the “single best time” to buy shares in the Elon Musk-led company.“Remember the piece that we did with Larry Williams... a couple weeks ago which said this is the single best time to buy Tesla, right here, right now? That’s what you’r