update version number

[maven-release-plugin] copy for tag spanner-jdbc-1.1.6

Update README.md

[maven-release-plugin] copy for tag spanner-jdbc-1.1.5

[maven-release-plugin] copy for tag spanner-jdbc-1.1.4

[maven-release-plugin] copy for tag spanner-jdbc-1.1.3

[maven-release-plugin] copy for tag spanner-jdbc-1.1.2

[maven-release-plugin] copy for tag spanner-jdbc-1.1.1

[maven-release-plugin] copy for tag spanner-jdbc-1.1

[maven-release-plugin] copy for tag spanner-jdbc-1.0.14