Fix documentation for installing dependencies (#148)
Fix documentation for installing dependencies (#148)

This is a fixup of 18c9d0016a395324f2eb65f385f5a896c499f2fc where
the file extension was omitted. At least on macOS, it doesn't work.
GoogleChrome/wptdashboard,GoogleChrome/wptdashboard,GoogleChrome/wptdashboard