Update Syntaxes/Diff.plist to recognize .rej files

When using the command `git apply --reject *.patch`, rejected hunks that do not apply will be saved to a .rej file. This file just contains file diff hunks, so it would be useful for it to be syntax highlighted as such.
Match git hashes longer than 7 characters

This may happen if 7 characters is not enough to provide ambiguity.