scrape_supported_devices.py: avoid changes to SupportedProtocols.md (#1140)
scrape_supported_devices.py: avoid changes to SupportedProtocols.md (#1140)

* only rewrite SupportedProtocols.md if any changes are detected
* use date of last commit for generated header
markszabo/IRremoteESP8266,markszabo/IRremoteESP8266,markszabo/IRremoteESP8266,markszabo/IRremoteESP8266