linux: call fclose(), fix fdopen() memory leak
linux: call fclose(), fix fdopen() memory leak

Commit 6798876 ("linux: fix cpu count") switched the /proc/stat parser
to fdopen().  Use fclose() to close the file descriptor to avoid leaking
resources associated with the FILE struct.

PR-URL: https://github.com/libuv/libuv/pull/747
Reviewed-By: Saúl Ibarra Corretgé <8a7991f6950ea189abf159d6ec98d2fcc13dc5f6@gmail.com>

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