THRIFT-4902: Swift 4 and 5 compatibility (#1827)

diff --git a/lib/swift/Sources/TProtocol.swift b/lib/swift/Sources/TProtocol.swift
index b111e71..b4e5dbe 100644
--- a/lib/swift/Sources/TProtocol.swift
+++ b/lib/swift/Sources/TProtocol.swift
@@ -18,7 +18,6 @@
 */
 
 import Foundation
-//
 
 public enum TMessageType: Int32 {
   case call = 1
@@ -99,19 +98,19 @@
 }
 
 public extension TProtocol {
-  public func writeFieldValue(_ value: TSerializable, name: String, type: TType, id: Int32) throws {
+  func writeFieldValue(_ value: TSerializable, name: String, type: TType, id: Int32) throws {
     try writeFieldBegin(name: name, type: type, fieldID: id)
     try value.write(to: self)
     try writeFieldEnd()
   }
 
-  public func validateValue(_ value: Any?, named name: String) throws {
+  func validateValue(_ value: Any?, named name: String) throws {
     if value == nil {
       throw TProtocolError(error: .unknown, message: "Missing required value for field: \(name)")
     }
   }
   
-  public func readResultMessageBegin() throws {
+  func readResultMessageBegin() throws {
     let (_, type, _) = try readMessageBegin();
     if type == .exception {
       let x = try readException()
@@ -120,17 +119,17 @@
     return
   }
   
-  public func readException() throws -> TApplicationError {
+  func readException() throws -> TApplicationError {
     return try TApplicationError.read(from: self)
   }
   
-  public func writeException(messageName name: String, sequenceID: Int32, ex: TApplicationError) throws {
+  func writeException(messageName name: String, sequenceID: Int32, ex: TApplicationError) throws {
     try writeMessageBegin(name: name, type: .exception, sequenceID: sequenceID)
     try ex.write(to: self)
     try writeMessageEnd()
   }
   
-  public func skip(type: TType) throws {
+  func skip(type: TType) throws {
     switch type {
     case .bool:   _ = try read() as Bool
     case .i8:   _ = try read() as UInt8