remove blank char from blank line

Signed-off-by: Lai Jiangshan <jiangshanlai@gmail.com>

runtime-config.md

@@ -7,7 +7,7 @@ Presently there are `Prestart` and `Poststop`.
 
 * [`Prestart`](#pre-start) is a list of hooks to be run before the container process is executed
 * [`Poststop`](#post-stop)is a list of hooks to be run after the container process exits
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 Hooks allow one to run code before/after various lifecycle events of the container.
 Hooks MUST be called in the listed order.
 The state of the container is passed to the hooks over stdin, so the hooks could get the information they need to do their work.