fix nullable header/timeout/url arg

src/main/java/com/imyeyu/network/ProgressiveRequest.java

@@ -50,19 +50,19 @@ public class ProgressiveRequest extends FileRequest {
 
 	@Override
 	public ProgressiveRequest header(String key, String value) {
-		request.addHeader(key, value);
+		super.header(key, value);
 		return this;
 	}
 
 	@Override
 	public ProgressiveRequest token(String token) {
-		request.addHeader("Token", token);
+		super.token(token);
 		return this;
 	}
 
 	@Override
 	public ProgressiveRequest language(String langHeader) {
-		request.addHeader("Accept-Language", langHeader);
+		super.language(langHeader);
 		return this;
 	}