golangci-lint/CI: Bump versions and introduce new linters (#798)

* golangci-lint/CI: Bump versions

Fix remaining linter issues

* Specifically set AppVeyor version

* Fix the infamous typos 👀

* Add go env cmd to AppVeyor

* Add go version cmd to AppVeyor

* Specify AppVeyor image, adjust linters

* Update go get to go install due to deprecation

* Bump golangci-lint timeout time for AppVeyor

* Change NW contract to NQ

* Address nitters

* GetRandomPair -> Pair{}

* Address nits

* Address time nitterinos plus additional tweaks

* More time inception upgrades!

* Bending time and space

common/cache/cache_test.go

@@ -130,16 +130,14 @@ func TestRemove(t *testing.T) {
 
 func TestGetNewest(t *testing.T) {
 	lruCache := New(2)
-	k, _ := lruCache.getNewest()
-	if k != nil {
+	if k, _ := lruCache.getNewest(); k != nil {
 		t.Fatal("expected GetNewest() on empty cache to return nil")
 	}
 }
 
 func TestGetOldest(t *testing.T) {
 	lruCache := New(2)
-	k, _ := lruCache.getOldest()
-	if k != nil {
+	if k, _ := lruCache.getOldest(); k != nil {
 		t.Fatal("expected GetOldest() on empty cache to return nil")
 	}
 }