adjust Base64String

Make a few minor changes:

• sort Base64String alphabetically
	For consistency.
• change underlying type of Base64String to string
	This is similar to how githubv4.GitObjectID or githubv4.HTML
	use a string rather than graphql.String. The pattern is that
	named graphql types are used for equivalent types in githubv4,
	otherwise basic types are used.
• add a test case for NewBase64String in TestNewScalars
	For consistency.

scalar.go

@@ -20,12 +20,12 @@ import (
 // is resolved, native Go types can completely replace these.
 
 type (
+	// Base64String is a (potentially binary) string encoded using base64.
+	Base64String string
+
 	// Boolean represents true or false values.
 	Boolean graphql.Boolean
 
-	// Base64String is a (potentially binary) string encoded using base64.
-	Base64String graphql.String
-
 	// Date is an ISO-8601 encoded date.
 	Date struct{ time.Time }
 
@@ -105,12 +105,12 @@ func (x *X509Certificate) UnmarshalJSON(data []byte) error {
 	return fmt.Errorf("X509Certificate.UnmarshalJSON: not implemented")
 }
 
-// NewBoolean is a helper to make a new *Boolean.
-func NewBoolean(v Boolean) *Boolean { return &v }
-
 // NewBase64String is a helper to make a new *Base64String.
 func NewBase64String(v Base64String) *Base64String { return &v }
 
+// NewBoolean is a helper to make a new *Boolean.
+func NewBoolean(v Boolean) *Boolean { return &v }
+
 // NewDate is a helper to make a new *Date.
 func NewDate(v Date) *Date { return &v }
 

scalar_test.go

@@ -76,6 +76,9 @@ func equalError(a, b error) bool {
 }
 
 func TestNewScalars(t *testing.T) {
+	if got := githubv4.NewBase64String(""); got == nil {
+		t.Error("NewBase64String returned nil")
+	}
 	if got := githubv4.NewBoolean(false); got == nil {
 		t.Error("NewBoolean returned nil")
 	}