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/analysis/edit/edit.go

@@ -0,0 +1,83 @@
+// Package edit contains helpers for creating suggested fixes.
+package edit
+
+import (
+	"bytes"
+	"go/ast"
+	"go/format"
+	"go/token"
+
+	"golang.org/x/tools/go/analysis"
+	"honnef.co/go/tools/pattern"
+)
+
+// Ranger describes values that have a start and end position.
+// In most cases these are either ast.Node or manually constructed ranges.
+type Ranger interface {
+	Pos() token.Pos
+	End() token.Pos
+}
+
+// Range implements the Ranger interface.
+type Range [2]token.Pos
+
+func (r Range) Pos() token.Pos { return r[0] }
+func (r Range) End() token.Pos { return r[1] }
+
+// ReplaceWithString replaces a range with a string.
+func ReplaceWithString(old Ranger, new string) analysis.TextEdit {
+	return analysis.TextEdit{
+		Pos:     old.Pos(),
+		End:     old.End(),
+		NewText: []byte(new),
+	}
+}
+
+// ReplaceWithNode replaces a range with an AST node.
+func ReplaceWithNode(fset *token.FileSet, old Ranger, new ast.Node) analysis.TextEdit {
+	buf := &bytes.Buffer{}
+	if err := format.Node(buf, fset, new); err != nil {
+		panic("internal error: " + err.Error())
+	}
+	return analysis.TextEdit{
+		Pos:     old.Pos(),
+		End:     old.End(),
+		NewText: buf.Bytes(),
+	}
+}
+
+// ReplaceWithPattern replaces a range with the result of executing a pattern.
+func ReplaceWithPattern(fset *token.FileSet, old Ranger, new pattern.Pattern, state pattern.State) analysis.TextEdit {
+	r := pattern.NodeToAST(new.Root, state)
+	buf := &bytes.Buffer{}
+	format.Node(buf, fset, r)
+	return analysis.TextEdit{
+		Pos:     old.Pos(),
+		End:     old.End(),
+		NewText: buf.Bytes(),
+	}
+}
+
+// Delete deletes a range of code.
+func Delete(old Ranger) analysis.TextEdit {
+	return analysis.TextEdit{
+		Pos:     old.Pos(),
+		End:     old.End(),
+		NewText: nil,
+	}
+}
+
+func Fix(msg string, edits ...analysis.TextEdit) analysis.SuggestedFix {
+	return analysis.SuggestedFix{
+		Message:   msg,
+		TextEdits: edits,
+	}
+}
+
+// Selector creates a new selector expression.
+func Selector(x, sel string) *ast.SelectorExpr {
+	return &ast.SelectorExpr{
+		X:   &ast.Ident{Name: x},
+		Sel: &ast.Ident{Name: sel},
+	}
+}