Merge branch 'latest_iris' into 'master'

Fix the examples / solution files for latest Iris.

Closes #2

See merge request !1
3 jobs for master in 8 minutes and 45 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
failed #23789
fp
build-coq.8.6.1

00:01:12

passed #23788
fp
build-coq.8.7.2

00:07:37

passed #23787
fp
build-coq.8.8.2

00:07:29

 
Name Stage Failure
failed
build-coq.8.6.1 Build

<><> Synchronising pinned packages ><><><><><><><><><><><><><><><><><><><><><><>
[coq-iris-tutorial-popl18-builddep.~dev] no changes from file:///builds/iris/tutorial-popl18/build-dep

The following dependencies couldn't be met:
- coq-iris-tutorial-popl18-builddep -> coq-iris (= dev.2019-01-22.0.b85a3cfc & = dev) -> coq >= dev
no matching version

ERROR: Job failed: exit code 1