update Luv to 1.48 - 1.50

[Bilal2453]

Changes overview

• Added new string methods for WTF16.
• Moved constants into one section.
• Added udp_try_send2.
• Added thread_detach, uv.thread_setname, thread_getname, getrusage_thread.
• Modified uv.tty_set_mode to accept string values.