unix/variants: Change mip package to mip-cmdline.

mip-cmdline adds command-line support to mip, useful for the unix port, via
micropython -m mip ...

Signed-off-by: Damien George <damien@micropython.org>

ports/unix/variants/manifest.py

@@ -1 +1 @@
-require("mip")
+require("mip-cmdline")