Security hardening of the Wiki command replacer script

[jrfnl]

As per the inline comment in the build/wiki-command-replacer.sh script, this script can do with some additional security hardening:

PHP_CodeSniffer-documentation/build/wiki-command-replacer.sh

Line 30 in 93f71d1

#FIXME refuse to run commands with a semicolon / pipe / ampersand / sub-shell

[jrfnl]

I believe this is now fixed via #38.