fix issue: https://github.com/NLPchina/elasticsearch-sql/issues/258

[allwefantasy]

see: #258

Example

select * from xxx/locs where 'a' = 'b'

select * from xxx/locs where 'a' = 1

select * from xxx/locs where 1 > 1

Unit test

org.nlpcn.es4sql. SqlParserTests.numberEqualConditionWithoutProperty
org.nlpcn.es4sql. SqlParserTests.numberGreatConditionWithoutProperty
org.nlpcn.es4sql. SqlParserTests.stringEqualConditionWithoutProperty
org.nlpcn.es4sql. SqlParserTests.stringAndNumberEqualConditionWithoutProperty