Replace TimeZone keywords like UTC and EDT with generic uppercase match

This allows supporting all the TimeZone abbreviations, which are all
included between 2 and 5 characters according to this Wikipedia article:
https://en.wikipedia.org/wiki/List_of_time_zone_abbreviations

syntax/log.vim

@@ -50,8 +50,8 @@ syn match logDate '\(\(Mon\|Tue\|Wed\|Thu\|Fri\|Sat\|Sun\) \)\?\(Jan\|Feb\|Mar\|
 syn match logTime '\d\{2}:\d\{2}:\d\{2}\(\.\d\{2,6}\)\?\(\s\?[-+]\d\{2,4}\|Z\)\?\>' nextgroup=logTimeZone,logSysColumns skipwhite
 
 " Follows logTime, matches UTC or PDT 2019 or 2019 EDT
-syn match logTimeZone '\(UTC\|PDT\|EDT\|CDT\|GMT\|EST\|KST\)\( \d\{4}\)\?' contained
-syn match logTimeZone '\d\{4} \(UTC\|PDT\|EDT\|CDT\|GMT\|EST\|KST\)' contained
+syn match logTimeZone '[A-Z]\{2,5}/>\( \d\{4}\)\?' contained
+syn match logTimeZone '\d\{4} [A-Z]\{2,5}/>' contained
 
 
 " Entities