Fix warnings about implicit conversion loses integer precision

[dleehr]

$ pod spec lint

 -> DLSFTPClient (1.0.0)
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPConnection.m:356:93: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPConnection.m:363:33: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPConnection.m:368:33: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPConnection.m:373:33: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPConnection.m:849:31: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPDownloadRequest.m:106:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPMakeDirectoryRequest.m:76:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPMakeDirectoryRequest.m:99:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPListFilesRequest.m:77:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPMoveRenameRequest.m:75:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPMoveRenameRequest.m:98:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPRemoveDirectoryRequest.m:68:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPRemoveFileRequest.m:68:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPUploadRequest.m:79:25: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
    - NOTE  | [iOS] [xcodebuild]  DLSFTPClient/DLSFTPClient/Classes/DLSFTPUploadRequest.m:199:57: warning: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'int' [-Wshorten-64-to-32]