DOC: proxy-protocol: fix wrong byte in provided example

DOC: proxy-protocol: fix wrong byte in provided example

There was a mistake in the example of proxy-proto frame
provided, it cannot end with 0x02 but only 0x20 or 0x21
since the version is in the upper 4 bits and the lower ones
are 0 for LOCAL or 1 for PROXY, hence the example should be:

  \x0D\x0A\x0D\x0A\x00\x0D\x0A\x51\x55\x49\x54\x0A\x20

Thanks to Bram Grit for reporting this mistake.