This fixes some issues in crypto/signify and makes release signing work.

The archive signing step in ci.go used getenvBase64, which decodes the key data.
This is incorrect here because crypto/signify already base64-decodes the key.

* internal/build: implement signify's signing func
* Add signify to the ci utility
* fix output file format
* Add unit test for signify
* holiman's + travis' feedback
* internal/build: verify signify's output
* crypto: move signify to common dir
* use go-minisign to verify binaries
* more holiman feedback
* crypto, ci: support minisign output
* only accept one-line trusted comments
* configurable untrusted comments
* code cleanup in tests
* revert to use ed25519 from the stdlib
* bug: fix for empty untrusted comments
* write timestamp as comment if trusted comment isn't present
* rename line checker to commentHasManyLines
* crypto: added signify fuzzer (#6)
* crypto: added signify fuzzer
* stuff
* crypto: updated signify fuzzer to fuzz comments
* crypto: repro signify crashes
* rebased fuzzer on build-signify branch
* hide fuzzer behind gofuzz build flag
* extract key data inside a single function
* don't treat \r as a newline
* travis: fix signing command line
* do not use an external binary in tests
* crypto: move signify to crypto/signify
* travis: fix formatting issue
* ci: fix linter build after package move

Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>

This fixes cross-build and mobile framework failures.
It also disables the mac test builder because it was failing
all the time in hard to understand ways and we can't afford
it anymore under Travis CI's new pricing.

This new flag downloads a known version of Go and builds with it. This
is meant for environments where we can't easily upgrade the installed Go
version.

* .travis.yml: remove install step for PR test builders

We added this step originally to avoid re-building everything
for every test. go test has become much smarter in recent go
releases, so we no longer need to install anything here.

This PR makes use of go 1.13 error handling, wrapping errors and using
errors.Is to check a wrapped root-cause. It also removes the travis
builders for go 1.11 and go 1.12.

* travis, appveyor, build, Dockerfile: bump Go to 1.14.2

* travis, appveyor: force GO111MODULE=on for every build

* travis: remove debug traces

* travis: Add travis_wait to the test run

* travis: increase travis_wait time

* build: use golangci-lint

This changes build/ci.go to download and run golangci-lint instead
of gometalinter.

* core/state: fix unnecessary conversion

* p2p/simulations: fix lock copying (found by go vet)

* signer/core: fix unnecessary conversions

* crypto/ecies: remove unused function cmpPublic

* core/rawdb: remove unused function print

* core/state: remove unused function xTestFuzzCutter

* core/vm: disable TestWriteExpectedValues in a different way

* core/forkid: remove unused function checksum

* les: remove unused type proofsData

* cmd/utils: remove unused functions prefixedNames, prefixFor

* crypto/bn256: run goimports

* p2p/nat: fix goimports lint issue

* cmd/clef: avoid using unkeyed struct fields

* les: cancel context in testRequest

* rlp: delete unreachable code

* core: gofmt

* internal/build: simplify DownloadFile for Go 1.11 compatibility

* build: remove go test --short flag

* .travis.yml: disable build cache

* whisper/whisperv6: fix ineffectual assignment in TestWhisperIdentityManagement

* .golangci.yml: enable goconst and ineffassign linters

* build: print message when there are no lint issues

* internal/build: refactor download a bit

* travis: Enable ARM support

* Include fixes from 20039

* Add a trace to debug the invalid lookup issue

* Try increasing the timeout to see if the arm test passes

* Investigate the resolver issue

* Increase arm64 timeout for clique test

* increase timeout in tests for arm64

* Only test the failing tests

* Review feedback: don't export epsilon

* Remove investigation tricks+include fjl's feeback

* Revert the retry ahead of using the mock resolver

* Fix rebase errors

* build: bump PPAs to Go 1.13 (via longsleep), keep Trusty on 1.11

* travis, build, vendor: use own Go bundle for PPA builds

* travis, build, internal, vendor: smarter Go bundler, own untar

* build: updated ci-notes with new Go bundling, only make, don't test