Set up Travis CI for release binaries

[ahmetb]

Ref: #324.
Ref: #333.

Fixes #337.
/assign @corneliusweig

[codecov-io]

Codecov Report

Merging #334 into master will decrease coverage by 0.11%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #334      +/-   ##
==========================================
- Coverage   56.89%   56.78%   -0.12%     
==========================================
  Files          19       19              
  Lines         907      907              
==========================================
- Hits          516      515       -1     
- Misses        338      339       +1     
  Partials       53       53

Impacted Files	Coverage Δ
cmd/validate-krew-manifest/main.go	55.1% <0%> (-1.03%)	⬇️

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[corneliusweig]

As far as I can tell, this looks good. I only have little experience with releasing via travis on Github, though. Can we somehow test this before merging?

One minor nit: Before, we were building with golang:alpine-1, which uses golang 1.13 (see https://github.com/docker-library/golang/blob/2909cfd3ecb769671eb8222eaf9a782a6aed024d/1.13/alpine3.10/Dockerfile). On Travis, we are still using golang 1.11. Can we bump that for our travis builds?

[corneliusweig]

PS: It would make sense to also adapt hack/make-release-notes.sh with the new download URLs for the krew artifacts.

[ahmetb]

I've tagged a v0.3.0-rc.1 with this commit. I've manually marked it as pre-release.
Sadly, there's still no clean way to auto-populate release message (#122) but it works.

[ahmetb]

Addressed comments.

[ahmetb]

I'm getting some weird errors after switching go: 1.13.x, might go back to 1.11.x.

[corneliusweig]

/lgtm
/approve
Big 👍 for getting the migration to Travis done so quickly AND fixing this strange flags.Parse() bug.

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[corneliusweig]

Btw, with github releases we can get the number of downloads pretty easily:

curl -sLH 'Accept: application/vnd.github.v3+json' "https://api.github.com/repos/kubernetes-sigs/krew/releases" | \
        jq 'map([{key: "release", value: .tag_name}, {key: "assets", value: ( .assets | map({key: .name, value: .download_count}) | from_entries )}]|from_entries) '

At least we will know how many users upgraded krew :)

[ahmetb]

Exactly my thoughts.

I wish we had an app that monitored that endpoint it over time so we could tell the delta by {day, month, year} to do some analytics.

I have developed https://gh-downloads-dpyb4duzqq-uc.a.run.app/grpc-ecosystem/grpc-health-probe many months ago but it doesn't have any sort of persistent storage.