fix pattern for java stacktrace (elastic#13516) (elastic#16745)

this patch fix regex patter for adding last line of java stacktrace with contains line with "..."

Co-authored-by: Alex <theshamuel@gmail.com>

filebeat/docs/multiline.asciidoc

@@ -123,7 +123,7 @@ To consolidate these lines into a single event in {beatname_uc}, use the followi
 
 [source,yaml]
 -------------------------------------------------------------------------------------
-multiline.pattern: '^[[:space:]]+(at|\.{3})\b|^Caused by:'
+multiline.pattern: '^[[:space:]]+(at|\.{3})[[:space:]]+\b|^Caused by:'
 multiline.negate: false
 multiline.match: after
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