file exists check for scp

[SytzeAndr]

Hi,

For me the file exists did not seem to work properly as it was misclassifying all files as being non-existent, resulting in some unnecessary updating.

It seemed the original check, i.e. checking if the string equals "1" did always returned false. This PR replaces it with a check on just the first character.

The exact cause is unknown for me, but I assume some trailing characters exist by using chomp on a plain "1". Maybe some dependency has changed behavior. It's a bit unclear to me but in general I think this is more stable.

Ruby version: ruby 2.6.6p146 (2020-03-31 revision 67876) [x64-mingw32]