Fix: Random Delimiter in CSV Parser

[SijieMei]

Issue

test testDelimiterDiscovery randomly failed due to the output is not "1", "2;2", "3;3", "4;a" but "1,2", "2,3", "3,4", "a".

Reason

In the CSV Parser, we use several rules to determine the delimiter. like if the optional delimiter exists in all rows or how many times the delimiter exists in the current row. If there are two optional delimiters met all rules with the same weight, they will remain in the method "pickDelimiter" in "CsvFormatDetector.java". Since we use a HashSet to store all delimiters, one delimiter will be randomly output.

Change

Use LinkedHashSet instead of HashSet so the out delimiter will be the same in different runs.