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/internal/sync/sync.go

@@ -0,0 +1,36 @@
+package sync
+
+type Semaphore struct {
+	ch chan struct{}
+}
+
+func NewSemaphore(size int) Semaphore {
+	return Semaphore{
+		ch: make(chan struct{}, size),
+	}
+}
+
+func (sem Semaphore) Acquire() {
+	sem.ch <- struct{}{}
+}
+
+func (sem Semaphore) AcquireMaybe() bool {
+	select {
+	case sem.ch <- struct{}{}:
+		return true
+	default:
+		return false
+	}
+}
+
+func (sem Semaphore) Release() {
+	<-sem.ch
+}
+
+func (sem Semaphore) Len() int {
+	return len(sem.ch)
+}
+
+func (sem Semaphore) Cap() int {
+	return cap(sem.ch)
+}