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

currency/code_test.go

@@ -51,8 +51,7 @@ func TestRoleMarshalJSON(t *testing.T) {
 		t.Error("Role MarshalJSON() error", err)
 	}
 
-	expected := `"fiatCurrency"`
-	if string(d) != expected {
+	if expected := `"fiatCurrency"`; string(d) != expected {
 		t.Errorf("Role MarshalJSON() error expected %s but received %s",
 			expected,
 			string(d))
@@ -337,18 +336,14 @@ func TestBaseCode(t *testing.T) {
 }
 
 func TestCodeString(t *testing.T) {
-	expected := "TEST"
-	cc := NewCode("TEST")
-	if cc.String() != expected {
+	if cc, expected := NewCode("TEST"), "TEST"; cc.String() != expected {
 		t.Errorf("Currency Code String() error expected %s but received %s",
 			expected, cc)
 	}
 }
 
 func TestCodeLower(t *testing.T) {
-	expected := "test"
-	cc := NewCode("TEST")
-	if cc.Lower().String() != expected {
+	if cc, expected := NewCode("TEST"), "test"; cc.Lower().String() != expected {
 		t.Errorf("Currency Code Lower() error expected %s but received %s",
 			expected,
 			cc.Lower())
@@ -356,9 +351,7 @@ func TestCodeLower(t *testing.T) {
 }
 
 func TestCodeUpper(t *testing.T) {
-	expected := "TEST"
-	cc := NewCode("test")
-	if cc.Upper().String() != expected {
+	if cc, expected := NewCode("test"), "TEST"; cc.Upper().String() != expected {
 		t.Errorf("Currency Code Upper() error expected %s but received %s",
 			expected,
 			cc.Upper())