opam: add dependency on bubblewrap.

[chris@cmbvm ~]$ opam init
[NOTE] Will configure from built-in defaults.
Checking for available remotes: rsync and local, git.
  - you won't be able to use mercurial repositories unless you install
    the hg     command on your system.
  - you won't be able to use darcs repositories unless you install
    the darcs     command on your system.

[ERROR] Missing dependencies -- the following commands are required
for opam to         operate:
  - bwrap: Sandboxing tool bwrap was not found. You should install
    'bubblewrap'. See
    https://opam.ocaml.org/doc/FAQ.html#Why-does-opam-require-bwrap.

srcpkgs/opam/template

@@ -1,13 +1,13 @@
 # Template file for 'opam'
 pkgname=opam
 version=2.0.8
-revision=1
+revision=2
 build_style=gnu-configure
 configure_args="--docdir=/usr/share/doc/${pkgname}"
 make_build_args="lib-ext all"
 make_check_target="tests"
 makedepends="curl ncurses-devel ocaml ocaml-findlib tar"
-depends="curl patch unzip"
+depends="bubblewrap curl patch unzip"
 checkdepends="${depends} git rsync"
 short_desc="OCaml package manager"
 maintainer="Leah Neukirchen <leah@vuxu.org>"