Hello,
yesterday I got my (first) Arduino MKR1000 and installed the tools and drivers via the "Board Manager".
Today I got the message in the IDE about updateable libraries. One of them was USBHost, which came with the board tools.
I've updated it to the newest version, but it doesn't disappear from the list for updateable libs. Because the original version 1.0 is installed in "$[HOME}/.arduino15/packages/arduino/hardware/samd/1.6.17/libraries/USBHost", while the updated version 1.0.5 is installed in "$[HOME}/Arduino/libraries/USBHost".