The Tonight Show house band The Roots had to cancel their SXSW concert tonight at Austin’s Fair Market due to a bomb threat. At first, local news sources were saying that the Grammy-winning band had to cancel their concert due to a “security concern.” The Austin Chronicle then reported that the abrupt cancelation was due to a bomb threat. Roots drummer Questlove tweeted about the cancellation of the concert and then posted an Instagram story (which has since been deleted)…