Upgrade go minimum to 1.13

[morgo]

This bumps the minimum golang version to 1.13. For prior art, the PR to bump to 1.12 was #5017

There are a couple of differences:

• We no longer support vagrant (I've skipped it)
• We no longer use travis
• We no longer support keytar

I have also grepped for 1.12, and here is the result:

morgo@morgox1:~/vitess$ grep -RF 1.12 .
./go/vt/vttablet/endtoend/main_test.go:insert into vitess_test_debuguser values(1, 1.12345, 0xC2A2, 0x00FF), (2, null, '', null), (3, null, null, null);
./go/vt/vttablet/endtoend/main_test.go:insert into vitess_test values(1, 1.12345, 0xC2A2, 0x00FF), (2, null, '', null), (3, null, null, null);
./go/vt/vttablet/endtoend/compatibility_test.go:				sqltypes.TestValue(sqltypes.Float32, "1.12345"),
./go.sum:github.com/go-ini/ini v1.12.0 h1:K324HQuOp7fYRWIW84d39Y7MqlH/0JU9fImSXUJ2TWk=
./go.sum:github.com/go-ini/ini v1.12.0/go.mod h1:ByCAeIL28uOIIG0E3PJtZPDL8WnHpFKFOtgjp+3Ies8=
./go.sum:gopkg.in/resty.v1 v1.12.0/go.mod h1:mDo4pnntr5jdWRML875a/NmxYqAlA73dVijT2AXvQQo=
./web/vtctld2/package-lock.json:                          "version": "1.12.2",
./web/vtctld2/package-lock.json:      "version": "1.12.0",
./web/vtctld2/package-lock.json:      "resolved": "https://registry.npmjs.org/es-abstract/-/es-abstract-1.12.0.tgz",
./web/vtctld2/package-lock.json:        "mime-types": "^2.1.12"
./web/vtctld2/package-lock.json:      "version": "1.1.12",
./web/vtctld2/package-lock.json:      "resolved": "https://registry.npmjs.org/ieee754/-/ieee754-1.1.12.tgz",
./web/vtctld2/package-lock.json:      "version": "1.12.0",
./web/vtctld2/package-lock.json:      "resolved": "https://registry.npmjs.org/inflection/-/inflection-1.12.0.tgz",
./web/vtctld2/package-lock.json:        "body-parser": "^1.12.4",
./web/vtctld2/package-lock.json:            "mime-types": "^2.1.12"
./web/vtctld2/package-lock.json:            "mime-types": "^2.1.12"
./web/vtctld2/package-lock.json:            "mime-types": "^2.1.12"
./web/vtctld2/package-lock.json:        "dashdash": "^1.12.0",
./web/vtctld2/package-lock.json:      "version": "1.12.2",
./web/vtctld2/package-lock.json:      "resolved": "https://registry.npmjs.org/webpack-dev-middleware/-/webpack-dev-middleware-1.12.2.tgz",
./vagrant-scripts/bootstrap_vm.sh:GO_VER='1.12.7'
./examples/are-you-alive/build/dev/Dockerfile:FROM golang:1.12.5 AS build
./examples/are-you-alive/build/dev/Dockerfile:FROM golang:1.12.5-alpine AS runtime
./examples/are-you-alive/build/release/Dockerfile:FROM golang:1.12.5 AS build
./examples/are-you-alive/go.mod:go 1.12

I have skipped the example 'are-you-alive' because it is a standalone example (and I have not tried testing it), but I am happy to include it if reviewers deem necessary.

Signed-off-by: Morgan Tocker tocker@gmail.com

[morgo]

Waiting on #5944 and then I'll rebase.

[derekperkins]

I'm particularly looking forward to 1.14. Given how many places we're using defer, I imagine that there will be some noticeable performance improvements.

This release improves the performance of most uses of defer to incur almost zero overhead compared to calling the deferred function directly. As a result, defer can now be used in performance-critical code without overhead concerns.

[derekperkins]

No idea on the are you alive setup, but otherwise 👍