staticcheck (#313)

* CI: use staticcheck for linting

This commit switches the linter for Go code from golint to staticcheck.
Golint has been deprecated since last year and staticcheck is a
recommended replacement.

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

* revendor

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

* cmd,pkg: fix lint warnings

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

vendor/honnef.co/go/tools/cmd/staticcheck/README.md

@@ -0,0 +1,15 @@
+# staticcheck
+
+_staticcheck_ offers extensive analysis of Go code, covering a myriad
+of categories. It will detect bugs, suggest code simplifications,
+point out dead code, and more.
+
+## Installation
+
+See [the main README](https://github.com/dominikh/go-tools#installation) for installation instructions.
+
+## Documentation
+
+Detailed documentation can be found on
+[staticcheck.io](https://staticcheck.io/docs/).
+

vendor/honnef.co/go/tools/cmd/staticcheck/staticcheck.go

@@ -0,0 +1,45 @@
+// staticcheck analyses Go code and makes it better.
+package main
+
+import (
+	"log"
+	"os"
+
+	"honnef.co/go/tools/lintcmd"
+	"honnef.co/go/tools/lintcmd/version"
+	"honnef.co/go/tools/quickfix"
+	"honnef.co/go/tools/simple"
+	"honnef.co/go/tools/staticcheck"
+	"honnef.co/go/tools/stylecheck"
+	"honnef.co/go/tools/unused"
+)
+
+func main() {
+	cmd := lintcmd.NewCommand("staticcheck")
+	cmd.SetVersion(version.Version, version.MachineVersion)
+
+	fs := cmd.FlagSet()
+	debug := fs.String("debug.unused-graph", "", "Write unused's object graph to `file`")
+	qf := fs.Bool("debug.run-quickfix-analyzers", false, "Run quickfix analyzers")
+
+	cmd.ParseFlags(os.Args[1:])
+
+	cmd.AddAnalyzers(simple.Analyzers...)
+	cmd.AddAnalyzers(staticcheck.Analyzers...)
+	cmd.AddAnalyzers(stylecheck.Analyzers...)
+	cmd.AddAnalyzers(unused.Analyzer)
+
+	if *qf {
+		cmd.AddAnalyzers(quickfix.Analyzers...)
+	}
+
+	if *debug != "" {
+		f, err := os.OpenFile(*debug, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+		if err != nil {
+			log.Fatal(err)
+		}
+		unused.Debug = f
+	}
+
+	cmd.Run()
+}