Grammar fix

Author: andrewheard

FirebaseVertexAI/Sources/FunctionCalling.swift

@@ -36,7 +36,7 @@ public struct FunctionDeclaration {
   ///   - description: A brief description of the function.
   ///   - parameters: Describes the parameters to this function.
   ///   - optionalParameters: The names of parameters that may be omitted by the model in function
-  ///   calls; by default all parameters are considered required.
+  ///   calls; by default, all parameters are considered required.
   public init(name: String, description: String, parameters: [String: Schema],
               optionalParameters: [String] = []) {
     self.name = name