autorevision: use sed word delimiters for better precision

Fixes wrongly replaced 'cat' in help text:

$ autorevision -h
usage: autorevision {-t output-type | -s symbol} [-o cache-file [-f] ] [-e name] [-U] [-V]
	Options include:
	-t output-type		= specify output type
	-s symbol		= specify symbol output
	-o cache-file		= specify cache file lo/nix/store/1rzzq2wdn5vfgbp5y9613jpdkf8i9ag6-coreutils-8.26/bin/cation
...

(Also replace all occurences per line, in case that should occur.)