[ Travis ] Add .travis.yml to maintenance...

...just for the sake of having travis not complain about the
.travis.yml.  Note that maint-2.4.2 right now doesn't build on travis
because it needs modifications on master.
Merge branch 'maint-2.4.2' of https://github.com/agda/agda into maint-2.4.2
[ .gitignore ] Sorted entries
[ .gitignore ] Fixed sort
Merge branch 'maint-2.4.2'

Conflicts:
	.gitignore