In a telling reflection of growing institutional demand for cryptocurrencies, Bitcoin (CRYPTO: BTC) spot exchange-traded funds in the U.S. attracted net inflows for a record-breaking 18th day. What Happened: The 11 investment vehicles tracking the spot prices of the world’s largest digital asset saw $217.78 million in positive flows on June 5, according to data from SoSo Value. With this, the total inflows since the ETFs started trading in early January increased to $15.56 billion. More than $62 billion worth of Bitcoins backed these funds, representing 4.47% of its total circulating supply. T…