Migrate to go modules

[coolaj86]

Re: #5044

• remove a few unused modules (bolt, gorilla)
• go mod init and go mod tidy (adds go.mod and go.sum)
• remove Gopkg.*
• update drone file? (doesn't look like there was much to do)

[jonasfranz]

IMHO we shouldn't remove the vendor dir.
If a dependency or its host goes down, we can't build Gitea anymore.

[jonasfranz]

Please update the makefile in order to make sure that our CI tasks are going to work.

[jonasfranz]

Don't remove the vendor and test-vendor tasks.

[jonasfranz]

Aren't these changes from https://github.com/go-gitea/gitea/pull/5068/files#diff-da541ef36e39344f2e12bddd91d363e2 ?

[lunny]

Since Gitea depends on so many Go libraries. I would like to keep vendor to use go mod vendor.

[appleboy]

@coolaj86 Add build test in Drone

  build-with-go-module:
    image: golang:1.11
    pull: true
    environment:
      - TAGS="bindata sqlite"
      - GO111MODULE=on
    commands:
      - make clean
      - make generate
      - make build
    when:
      event: [ push, tag, pull_request ]

[xor-gate]

As @lunny suggests indeed it is good to cache also in the vendor folder. Because when somebody decides to pull the plug out of a dependency you are screwed.

[techknowlogick]

Can you keep this pegged at 1.9 as it is currently the oldest version of go that is supported.

[techknowlogick]

(but the others can remain at 1.11 as we just need to ensure that 1.9 builds, but we will distribute the versions of gitea that are built with a more recent version)

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 months. Thank you for your contributions.

[techknowlogick]

Closing due to #5743