all: drop support for go 1.10

[leighmcculloch]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

Summary

Drop support for Go 1.10, which makes the official supported versions:

• Go 1.11
• Go 1.12

Goal and scope

The code in this repository is used in critical systems and we should encourage its use with versions of Go that receive security updates.

The officially supported versions of Go are only the last two releases. Right now the last release is Go 1.12, and so only that version and the version prior are supported. Versions prior to 1.11 do not get security updates.

We also plan to move to using Go Modules instead of Go Dep for dependency management. Go Modules are only supported in Go 1.11 onwards.

Summary of changes

• Remove CI jobs that ran checks and tests on Go 1.10.
• Remove mentions of Go 1.10 in scripts.
• Replace any Dockerfiles using Go 1.10 with using the latest version of Go.
• Replace mentions of Go 1.10 being the min supported version, and replaced with Go 1.11.
• Add explanation of what versions of Go are supported and how that is determined to the top-level README.
• Add CHANGELOG entries to all services and released packages (txnbuild, horizon client).

Known limitations & issues

N/A

Related

Closes #1548
Related to #1542
Required for #1634

[leighmcculloch]

Note: check_code_1_10 and test_code_1_10 won't run because they were removed in this change.

[leighmcculloch]

@bartekn @brahman81 You two were mentioned as folks I should check in with before I finalize this change. Could you take a look, I think mostly a sanity check?

[brahman81]

This seems good to me, internally we are already building using 1.11.