fix spec/examples/parse-apache-logs failure due to QUOTEDSTRING not matching empty ""

Author: jordansissel

patterns/grok-patterns

@@ -14,7 +14,7 @@ SPACE \s*
 DATA .*?
 GREEDYDATA .*
 #QUOTEDSTRING (?:(?<!\\)(?:"(?:\\.|[^\\"])*"|(?:'(?:\\.|[^\\'])*')|(?:`(?:\\.|[^\\`])*`)))
-QUOTEDSTRING (?>(?<!\\)(?>"(?>\\.|[^\\"]+)+"|(?>'(?>\\.|[^\\']+)+')|(?>`(?>\\.|[^\\`]+)+`)))
+QUOTEDSTRING (?>(?<!\\)(?>"(?>\\.|[^\\"]+)+"|""|(?>'(?>\\.|[^\\']+)+')|''|(?>`(?>\\.|[^\\`]+)+`)|``))
 UUID [A-Fa-f0-9]{8}-(?:[A-Fa-f0-9]{4}-){3}[A-Fa-f0-9]{12}
 
 # Networking