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/github.com/BurntSushi/toml/deprecated.go

@@ -0,0 +1,33 @@
+package toml
+
+import (
+	"encoding"
+	"io"
+)
+
+// DEPRECATED!
+//
+// Use the identical encoding.TextMarshaler instead. It is defined here to
+// support Go 1.1 and older.
+type TextMarshaler encoding.TextMarshaler
+
+// DEPRECATED!
+//
+// Use the identical encoding.TextUnmarshaler instead. It is defined here to
+// support Go 1.1 and older.
+type TextUnmarshaler encoding.TextUnmarshaler
+
+// DEPRECATED!
+//
+// Use MetaData.PrimitiveDecode instead.
+func PrimitiveDecode(primValue Primitive, v interface{}) error {
+	md := MetaData{decoded: make(map[string]bool)}
+	return md.unify(primValue.undecoded, rvalue(v))
+}
+
+// DEPRECATED!
+//
+// Use NewDecoder(reader).Decode(&v) instead.
+func DecodeReader(r io.Reader, v interface{}) (MetaData, error) {
+	return NewDecoder(r).Decode(v)
+}