spanner-jdbc: JdbcTypeConverterTest failure

[skuruppu]

Tests in #73 fail as follows:

com.google.common.truth.ComparisonFailureWithFacts:
expected: 1969-12-31T22:59:59Z
but was : 1969-12-31T23:00:00Z
	at com.google.cloud.spanner.jdbc.JdbcTypeConverterTest.testToGoogleTimestamp(JdbcTypeConverterTest.java:608)

@olavloite if you could take a look that would be great.

[olavloite]

This is probably caused by https://www.github.com/googleapis/java-core/commit/1f8b6b4835aaa702ec94bbbde89ed90f519c935a (which is a good fix, BTW). I'll look into the test cases for the JDBC driver.