fix: add new line at the end of the platform's section in order to remove it correctly

[Fatme]

Steps to reproduce:

1. tns create myApp --js
2. tns plugin add nativescript-imagepicker && tns plugin add nativescript-facebook
3. Replace the content of ./node_modules/nativescript-imagepicker/platforms/ios/Podfile with platform: ios, '9.0'
4. Replace the content of ./node_modules/nativescript-facebook/platforms/ios/Podfile with platform: ios, '10.0'
5. Add Podfile in ./app/App_Resources/iOS with the following content platform: ios: '8.0'
6. Execute tns prepare ios
7. Remove ./app/App_Resources/iOS/Podfile
8. Execute tns prepare ios

Expected behavior: It should pass correctly and the content of platforms/ios/Podfile should be

...
# NativeScriptPlatformSection /node_modules/nativescript-facebook/platforms/ios/Podfile with 10.0
       platform :ios, '10.0'
# End NativeScriptPlatformSection
end

Actual behavior: It fails with [!] Invalid Podfile file: syntax error, unexpected end-of-input, expecting keyword_end. error and the the content of platforms/ios/Podfile is:

...
# NativeScriptPlatformSection /node_modules/nativescript-facebook/platforms/ios/Podfile with 10.0
       platform :ios, '10.0'
# End NativeScriptPlatformSectionend

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Fixes/Implements/Closes #[Issue Number].

Rel to: #3604