Trim lineendings from resulting strings

[pysco68]

It seems that when line endings are not in the expected format (for example when env file was checked out on a windows machine) it can happen that the read values are suffixed with a "remaining" `\r' (or another EOL char depending on platform mix & matching)

Example trace of a piece of code using dotenv-cpp (not \r afte ../../tipi_auto_deploy_postgrespassword.txt):

openat(AT_FDCWD, "../../tipi_auto_deploy_postgrespassword.txt\r", O_RDONLY) = -1 ENOENT (No such file or directory)
futex(0x7f1a47b2a1e0, FUTEX_WAKE_PRIVATE, 2147483647) = 0
write(2, "terminate called after throwing "..., 48terminate called after throwing an instance of ') = 48
write(2, "std::runtime_error", 18std::runtime_error)      = 18
write(2, "'\n", 2'
)