Fix README snippets

Author: jmagman

packages/pigeon/example/README.md

@@ -127,14 +127,14 @@ private class PigeonApiImplementation: ExampleHostApi {
   }
 
   func add(_ a: Int64, to b: Int64) throws -> Int64 {
-    if (a < 0 || b < 0) {
-      throw FlutterError(code: "code", message: "message", details: "details");
+    if a < 0 || b < 0 {
+      throw FlutterError(code: "code", message: "message", details: "details")
     }
     return a + b
   }
 
   func sendMessage(message: MessageData, completion: @escaping (Result<Bool, Error>) -> Void) {
-    if (message.code == Code.one) {
+    if message.code == Code.one {
       completion(.failure(FlutterError(code: "code", message: "message", details: "details")))
       return
     }