[pcre/en] fix domain name => protocol (#4902)

pcre.html.markdown

@@ -6,7 +6,7 @@ contributors:
 
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-A regular expression (regex or regexp for short) is a special text string for describing a search pattern. e.g. to extract domain name from a string we can say `/^[a-z]+:/` and it will match `http:` from `http://github.com/`.
+A regular expression (regex or regexp for short) is a special text string for describing a search pattern. e.g. to extract the protocol from a url string we can say `/^[a-z]+:/` and it will match `http:` from `http://github.com/`.
 
 PCRE (Perl Compatible Regular Expressions) is a C library implementing regex. It was written in 1997 when Perl was the de-facto choice for complex text processing tasks. The syntax for patterns used in PCRE closely resembles Perl. PCRE syntax is being used in many big projects including PHP, Apache, R to name a few.