Use most recent MK build and update sprint releases todo list

We want to make sure we perform this check at every release so that
when we build miniooni we use the latest MK.

.github/ISSUE_TEMPLATE/routine-sprint-releases.md

@@ -11,6 +11,8 @@ assignees: bassosimone
 - [ ] Update Host header used for measuring
 - [ ] Update version/version.go
 - [ ] Update assets
+- [ ] Update measurementkit/mkcgo/mkcgo.go
+- [ ] Update .github/workflows/mk.sh
 - [ ] Tag a new version of ooni/probe-engine
 - [ ] Update ooni/probe-engine mobile-staging branch
 - [ ] Pin ooni/probe-cli to ooni/probe-engine

.github/workflows/mk.yml

@@ -5,4 +5,4 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - run: docker run -v`pwd`:/mk -w/mk openobservatory/mk-alpine:20200226 /mk/.github/workflows/mk.sh
+      - run: docker run -v`pwd`:/mk -w/mk openobservatory/mk-alpine:20200513 /mk/.github/workflows/mk.sh