ucode: update to latest Git HEAD

ucode: update to latest Git HEAD

4ae7072 fs: use `getline()` for line wise read operations
21ace5e lexer: fixes for regex literal parsing
00965fa lib: implement slice() function
76d396d main: implement print mode
7bbba78 compiler: optimize function return opcode generation
a45f2a3 lexer: improve regex literal handling
d64d5d6 vm: maintain export symbol tables per program
f4b4ded uloop: task: gracefully handle absent output callback
a58fe47 ubus: hold reference to underlying connection until deferred is concluded
e23b58a lib: uc_system(): retry waitpid() on EINTR
cc4eb79 ubus: support obtaining numeric error code
01c412c ubus: add toplevel constants for ubus status codes
8e240fa ubus: allow object method call handlers to return a numeric status code
5cdddd3 lib: add limit support to split() and replace()
0ba9c3e fs: add optional third permission argument to fs.open()
c1f7b3b lib: remove fixed capture group limit in match() and regex replace()

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(backported from commits 639754e36d849553e288f8e34f51f793761c07db
 and 5110dcb1fa44fc1aac737c63b31474daa471de89)