alert_words: Revert back `before_punctuation` regex to stable one.
alert_words: Revert back `before_punctuation` regex to stable one.

In this 009b7bca24112bf4d429fe8f01e62edf8fc130ba commit `before_punctuation`
regex was updated to use lookbehind feature of regex.

This caused a regex error in some browsers (reported in
Safari) because lookbehind feature is not yet supported
on all the browsers (https://caniuse.com/js-regexp-lookbehind).

This commit fixes that error by reverting to stable regex which
works on all the browsers.

punchagan/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,kou/zulip,punchagan/zulip,kou/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,punchagan/zulip,kou/zulip,kou/zulip,zulip/zulip,punchagan/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,hackerkid/zulip